Network Security -4

1 Virus Types and Attacks

Understanding what a virus is, how it spreads, and the different variations is essential for defending against virus threats. You will also need to understand how a virus scanner works in order to make intelligent decisions about purchasing a virus scanner for your organisation.

8.1.1 What is a Virus

Most people are familiar with computer viruses, but may not have a clear definition of what is. A computer virus is a program that self-replicates. A virus will also have some other negative functions such as deleting files or changing system settings. However, the self-replication and rapid spread that define a virus. Often this growth, in and of itself, can be a problem for an infected network. It can lead to excessive network traffic and prevent the network from functioning properly. The more a virus floods a network with traffic, the less capacity is left for real work to be performed.

8.1.2 What is a Worm

A worm is a special type of virus. Some texts go to great lengths to differentiate worms and viruses, while others treat the worm as simply a subset of a virus. A worm is a virus that can spread without human intervention. In other words, a virus requires some human action in order to infect a machine (downloading a file, opening an attachment, and so on), but a worm can spread without such interaction. In recent years, worm eruptions have become more common than the standard, non-worm virus. Today most of what is called a “virus” is actually a worm.

8.1.3 How a Virus Spreads

The best way to combat viruses is to limit their spread, so it is critical that you understand how they spread. A virus will usually spread in one of two ways. The most common, and the simplest, method is to read your e-mail address book and e-mail itself to everyone in your address book. The second method is to simply scan your computer for connections to a network, and then copy itself to other machines on the network to which your computer has access. This is actually the most efficient way for a virus to spread, but it requires more programming skills than the other method.

The first method is, by far, the most common method for virus propagation. Microsoft Outlook may be the one e-mail program most often hit with such virus attacks. The reason is not so much a security flaw in Outlook, as it is the ease of working with Outlook.

Another way a virus can spread is by examining the affected system looking for any connected computers and copying itself to them. This sort of self-propagation does not require user interaction, so the program that uses this method to infect a system is classified as a worm.

Regardless of the way a virus arrives at your doorstep, once it is on your system, it will attempt to spread and, in many cases, will attempt to cause some harm to your system. Once a virus is on your system, it can do anything that any legitimate program can do. That means it could potentially delete files, change system settings, or cause other harm. The threat from virus attacks cannot be overstated. Some recent virus eruptions went so far as to disable existing security software, such as antivirus scanners and firewalls. Rombertik

Rombertik caused chaos in 2015. This malware uses the browser to read user credentials to websites. It is sent as an attachment to an e-mail. Perhaps even worse, in some situations Rombertik will either overwrite the master boot record on the hard drive, making the machine unbootable, or begin encrypting files in the user’s home directory. Shamoon

Shamoon is a computer virus discovered in 2012 designed to target computers running Microsoft Windows in the energy sector. Symantec, Kaspersky Lab, and Seculert announced its discovery on August 16, 2012. It is essentially a data-stealing program that seems to target systems in energy companies. A variant of Shamoon appeared again in 2017.

Several other viruses, worm and malware exist such as Gameover Zeus, Mirai, Linux Encoder 1, Kedi RAT and much more. Ransomware


It is impossible in modern times to discuss malware and not discuss ransomware. While many people first began discussing ransomware with the advent of CrytpoLocker in 2103, ransomware has been around a lot longer than that. The first known ransomware was the 1989 PC Cyborg Trojan, which only encrypted filenames with a weak symmetric cipher. In early 2017 the WannaCry ransomware spread, starting in health care systems in the United Kingdom. It attacked unpatched Windows systems. This states the need for patching.

The Bad Rabbit computer virus spread in late 2017. This virus is ransomware. It began attacking in Russia and Ukraine, but quickly spread around the world.

8.1.4 Types of Viruses

There are many types of viruses. A virus can be classified by either its propagation method or by its activities on the target computers.

  • Macro: Macro viruses infect the macros in office documents. Many office products, including Microsoft Office, allow users to write mini-programs called macros. These macros can also be written as a virus. A macro virus is written into a macro in some business application. For example, Microsoft Office allows users to write macros to automate some tasks. Microsoft Outlook is designed so that a programmer can write scripts using a subset of the Visual Basic programming language, called Visual Basic for Applications (VBA).
    This scripting language is, in fact, built into all Microsoft Office products. Programmers can also use the closely related VBScript language. Both languages are quite easy to learn. If such a script is attached to an e-mail and the recipient is using Outlook, then the script can execute. That execution can do any number of things, including scanning the address book, looking for addresses, sending out e-mail, deleting e-mail, and more.
  • Boot Sector: As the name suggests, a boot sector virus infects the boot sector of the drive, rather than the operating system. This makes them more difficult to eliminate, as most antivirus software works within the operating system.
  • Multipartite: Multipartite viruses attack the computer in multiple ways—for example, infecting the boot sector of the hard disk and one or more files.
  • Memory resident: A memory-resident virus installs itself and then remains in RAM from the time the computer is booted up to when it is shut down.
  • Armored: An Armored virus uses techniques that make it hard to analyse. Code confusion is one such method. The code is written such that if the virus is disassembled, the code won’t be easily followed. Compressed code is another method for armouring the virus.
  • Stealth: There are several types of stealth virus. A stealth virus attempts to hide itself from antivirus. A few common methods of stealth are shown below:
    • Sparse infector: A sparse infector virus attempts to escape detection by performing its malicious activities only sporadically. With a sparse infector virus, the user will see symptoms for a short period, then no symptoms for a time. In some cases the sparse infector targets a specific program but the virus only executes every 10th time or 20th time that target program executes. Or a sparse infector may have a burst of activity and then lie dormant for a period of time. There are a number of variations on the theme, but the basic principle is the same: to reduce the frequency of attack and thus reduce the chances for detection.
    • Encrypted: Sometimes a virus is encrypted, even with weak encryption, just enough to prevent an antivirus program from recognizing the virus. Then when it is time to launch an attack, the virus is decrypted.
    • Polymorphic: A polymorphic virus literally changes its form from time to time to avoid detection by antivirus software. A more advanced form of this is called the metamorphic virus; it can completely change itself.




8.2 Virus Scanners

The most obvious defence against viruses is the virus scanner. A virus scanner is essentially software that tries to prevent a virus from infecting your system. Usually it scans incoming e-mail and other incoming traffic. Most virus scanners also have the ability to scan portable media devices such as USB drives.

In general, virus scanners work in two ways. The first method is that they contain a list of all known virus files. Generally, one of the services that vendors of virus scanners provide is a periodic update of this file. This list is typically in a small file, often called a .dat file (short for data). When you update your virus definitions, what actually occurs is that your current file is replaced by the more recent one on the vendor’s website.

The antivirus program then scans your PC, network, and incoming e-mail for known virus files. Any file on your PC or attached to an e-mail is compared to the virus definition file to see whether there are any matches. With e-mail, this can be done by looking for specific subject lines and content. Known virus files often have specific phrases in the subject line and the body of the messages they are attached to. Yet viruses and worms can have a multitude of headers, some of which are very common, such as re:hello or re:thanks.

Scanning against a list of known viruses alone would result in many false positives. Therefore, the virus scanner also looks at attachments to see whether they have a certain size and creation date that matches a known virus or whether it contains known viral code. The file size, creation date, and location are the tell-tale signs of a virus. Depending on the settings of your virus scanner, you may be prompted to take some action, the file may be moved to a quarantined folder, or the file may simply be deleted outright. This type of virus scanning works only if the .dat file for the virus scanner is updated, and only for known viruses.

Another way a virus scanner can work is to monitor your system for certain types of behaviour that are typical of a virus. This might include programs that attempt to write to a hard drive’s boot sector, change system files, alter the system registry, automate e-mail software, or self-multiply. Another technique virus scanners often use is searching for files that stay in memory after they execute. This is called a Terminate and Stay Resident (TSR) program. Some legitimate programs do this, but it is often a sign of a virus.

Many virus scanners have begun employing additional methods to detect viruses. Such methods include scanning system files and then monitoring any program that attempts to modify those files. This means the virus scanner must first identify specific files that are critical to the system. With a Windows system, these include the registry, the boot.ini, and possibly other files. Then, if any program attempts to alter these files, the user is warned and must first authorize the alteration before it can proceed.

It is also important to differentiate between on-demand virus scanning and ongoing scanners. An ongoing virus scanner runs in the background and is constantly checking a PC for any sign of a virus. On-demand scanners run only when you launch them. Most modern antivirus scanners offer both options.

8.2.1 Email and Attachment Scanning

Since the primary propagation method for a virus is e-mail, e-mail and attachment scanning is the most important function of any virus scanner. Some virus scanners actually examine your e-mail on the e-mail server before downloading it to your machine. Other virus scanners work by scanning your e-mail and attachments on your computer before passing it to your e-mail program. In either case, the e-mail and its attachments should be scanned prior having any chance to open it and release the virus on your system. This is a critical difference. If the virus is first brought to your machine, and then scanned, there is a chance, however small, that the virus will still be able to infect your machine. Most commercial network virus scanners will scan the e-mail on the server before sending it on to the workstations.

8.2.2 Download Scanning

Anytime you download anything from the Internet, either via a web link or with an FTP program, there is a chance you might download an infected file. Download scanning works much like e-mail and attachment scanning, but does so on files you select for downloading.

8.2.3 File Scanning

Download and e-mail scanning will only protect your system against viruses that you might get downloading from a site, or that come to you in e-mail. Those methods will not help with viruses that are copied over a network, deposited on a shared drive, or that are already on your machine before you install the virus scanner.

This is the type of scanning in which files on your system are checked to see whether they match any known virus. This sort of scanning is generally done on an on-demand basis instead of an ongoing basis. It is a good idea to schedule your virus scanner to do a complete scan of the system periodically. I personally recommend a weekly scan, preferably at a time when no one is likely to be using the computer.

It does take time and resources to scan all the files on a computer’s hard drive for infections. This type of scanning uses a method similar to e-mail and download scanning. It looks for known virus signatures. Therefore, this method is limited to finding viruses that are already known and will not find new viruses.

8.2.4 Heuristic Scanning

This is perhaps the most advanced form of virus scanning. This sort of scanning uses rules to determine whether a file or program is behaving like a virus, and is one of the best ways to find a virus that is not a known virus. A new virus will not be on any virus definition list, so you must examine its behaviour to determine whether it is a virus. However, this process is not fool proof. Some actual virus infections will be missed, and some non-virus files might be suspected of being a virus.

The unfortunate side effect of heuristic scanning is that it can easily lead to false positives. This means that it might identify a file as a virus, when in fact it is not. Most virus scanners do not simply delete viruses. They put them in a quarantined area, where you can manually examine them to determine whether you should delete the file or restore it to its original location. Examining the quarantined files rather than simply deleting them all is important because some can be false positives. In this author’s personal experience, false positives are relatively rare with most modern virus scanners.

As the methods for heuristic scanning become more accurate, it is likely that more virus scanners will employ this method, and will rely on it more heavily. Such algorithms are constantly being improved. One area of research now is adding machine learning to antivirus algorithms.

8.2.5 Active Code Scanning

Modern websites frequently embed active codes, such as Java applets and ActiveX. These technologies can provide some stunning visual effects to any website. However, they can also be vehicles for malicious code. Scanning such objects before they are downloaded to your computer is an essential feature in any quality virus scanner.

8.2.6 Instant Messaging Scanning

Instant message scanning is a relatively new feature of virus scanners. Virus scanners using this technique scan instant messaging communications looking for signatures of known virus or Trojan horse files. In recent years the use of instant messaging has increased dramatically. It is now frequently used for both business and recreational purposes. This growing popularity makes virus scanning for instant messaging a vital part of effective virus scanning. If your antivirus scanner does not scan instant messaging, then you should either avoid instant messaging or select a different antivirus package.

Most commercial virus scanners use a multi-modal approach to scanning. They employ a combination of most, if not all, of the methods we have discussed here. Any scanner that does not employ most of these methods will have very little value as a security barrier for your system.


8.3 Antivirus

There are a number of antivirus packages available for individual computers and for network-wide virus scanning. It is important to consider the following factors when purchasing a virus scanning solution for your own organisation or recommending a solution to a client:

  • Budget: Price should not be the only, or even the most important, consideration, but it certainly must be considered.
  • Vulnerability: An organisation with diverse users who frequently get e-mail from outside the organisation or download from the Internet will need more antivirus protection than a small similar group that uses the Internet only occasionally.
  • Skill: Whoever will ultimately use the product must be able to understand how to use it. Are you getting a virus scanner for a group of tech-savvy engineers or a group of end users who are unlikely to be technically proficient?
  • Technical: How does the virus scanner work? What methods does it use to scan? How often are the .dat files updated? How quickly does the vendor respond to new virus threats and release new .dat files?

All of these factors must be considered when selecting antivirus solutions. Too often security experts simply recommend a product they are familiar with, without doing significant research.

8.3.1 McAfee

McAfee is a well-known antivirus vendor. Their antivirus has been marketed under many names, including VirusScan, Endpoint Security, and Total Protection. This company offers solutions for the home user and large organisations. All of McAfee’s products have some common features, including e-mail scanning and file scanning. They also scan instant messaging traffic.

McAfee scans e-mail, files, and instant messaging for known virus signatures, and uses heuristic methods to locate new worms. Given the growing use of worms (in contrast with traditional viruses), this is an important benefit. McAfee offers a relatively easy download and install, and you can get a trial version from the company’s website.

8.3.2 Norton Antivirus

Norton Antivirus is also a widely known vendor of antivirus software. You can purchase Norton solutions for individual computers or for entire networks. Norton offers e-mail and file scanning, as well as instant messaging scanning. It also offers a heuristic approach to discovering worms and traditional signature scanning. Recent versions of Norton Antivirus have also added anti-spyware and anti-adware scanning, both very useful features. An additional interesting feature of Norton Antivirus is the pre-install scan. During the installation, the install program scans the machine for any virus infections that might interfere with Norton. Because it is becoming more common to find virus attacks that actually seek to disable antivirus software, this feature is very helpful

While Norton, like most antivirus vendors, offers versions for individual PCs and for entire networks, the individual version has a free trial version you can download and experiment with for 15 days without any charge.

8.3.3 Avast Antivirus

This product is offered free for home, non-commercial uses. You can download the product from the vendor’s website: You can also find professional versions, versions for Unix or Linux, and versions specifically for servers. Of particular interest is that this product is available in multiple languages including English, Dutch, Finnish, French, German, Spanish, Italian, and Hungarian.

If you download it, you can see that Avast opens up with a tutorial. This feature, combined with the fact that the home version is free, makes this a very attractive tool for the novice home user. The Multilanguage and multioperating system support make it attractive to many professionals. When it finds a virus, it sounds an alarm and then a voice states “Warning: There is a virus on your computer.”

8.3.4 AVG

AVG antivirus has become quite popular. One reason is that there is a free version of it as well as a commercial version.

AVG is robust and full-featured antivirus software. It integrates with e-mail clients such as Microsoft Outlook and it also filters web traffic and downloads.

8.3.5 Kaspersky

Kaspersky has been growing in popularity. It includes business and personal versions. Like most antivirus products, it also includes additional features not directly related to detecting viruses. For example, Kaspersky includes an encrypted password vault to keep your passwords in, if you want to.

8.3.6 Panda

Panda is available in both commercial editions and free versions. The commercial version also comes with anti-spyware. Like Norton and McAfee, you can get a personal firewall bundled with the antivirus software. This product is available in English, French, and Spanish. This wide range of features makes this product a robust and effective solution.

8.3.7 Malwarebytes

This product is available from There is a free version of the product and a paid premium version. Malwarebytes has a strong reputation in the industry, it is well regarded, and it is rather simple to use.

8.3.8 Antivirus Policies and Procedures

Antivirus scanners are not the only facet of protecting yourself against viruses. In fact, there are situations in which a virus scanner is simply not enough. You will need policies and procedures to complete your antivirus strategy. Policies and procedures are simply written rules that dictate certain actions that administrators and end users should take and other activities they should avoid. Below are listed some policies and procedures:

  • Always use a virus scanner. It costs only about $30 a year to keep your virus scanner updated. It can cost much more to not do it.
  • If you are not sure about an attachment, do not open it. When you have specifically requested a file from someone, then opening an attachment from that person is probably safe. However, unexpected attachments are always cause for concern.
  • Consider exchanging a code word with friends and colleagues. Tell them to put the code word in the title of the message if they wish to send you an attachment. Without the code word, do not open any attachment.
  • Be sceptical of any e-mail you are sent. Keeping e-mail to official traffic will help reduce your danger. Jokes, flash movies, and so on simply should not be sent on a company e-mail system.
  • Do not download files from the Internet. If you need a file downloaded, the IT department should do that, carefully scan the file, and then forward it to the user. If you feel compelled to download files you should follow two simple rules:
    • Only download from well-known, reputable sites.
    • Download to a machine that is off the network first. Then you can scan that system for viruses. In fact, if you do request your IT department to download something for you, this is likely to be the process they use.



8.4 Guided Exercise: Scanning for Viruses

Machines Windows 10

In this exercise, you are required to scan a zip file with an antivirus and identify if the file is malicious.

Open the desktop folder called Exercises and then the folder Malwarebytes. Double click the file mb3-setup-consumer, to install Malwarebytes.

On the windows Open File – Security Warning select Run.

On the User Account Control windows select Yes.

Click OK on the Select Setup Language

On the Setup – Malwarebytes window Select Personal computer and then click Continue

Click Agree and Continue on the Setup – Malwarebytes window.

Once the installation finishes click Finish on the Setup – Malwarebytes window

Click Scan Now on the Malwarebytes window. If you get a warning for network error just ignore it after the scan finishes.

Once the scan finishes you can observer that Malwarebytes was able to identify the file trojan simulator as a malicious file.

Guided Exercise Video


8.5 Virus Infection and Identification

The unfortunate reality is that no matter what steps you take to prevent virus infections, there is still a chance your system being infected with a virus. The next question is, what do you do? Some facets of your response will depend upon the severity of the virus and how far it has spread, but generally, you need to focus on three things:

  • Stopping the spread of the virus.
  • Removing the virus.
  • Finding out how the infection started.

8.5.1 Stopping the Spread of the Virus

In the event of a virus infection, the first priority is to stop the spread of the infection. How this is done will, depend on how far the virus has spread. If the virus has only affected one machine, you can simply disconnect that machine from the network. However, it is unlikely that you will detect a virus before it has spread beyond a single machine. Given that fact, you will generally wish to follow these steps:

  • If the infection is on a segment of a WAN, then immediately disconnect from that WAN connection.
  • If the infection is on a subnetwork, immediately disconnect that subnetwork.
  • If there are servers with sensitive data that are connected (in any way) to the infected machine (or machines), disconnect those servers. This will prevent loss of sensitive data.
  • If there are backup devices connected to the infected machine or machines, disconnect them. This will prevent your backup media from becoming infected.

Obviously, your goal is to avoid getting a virus on your system. However, if that unfortunate event occur, following these steps can minimize the damage and get your system back up and functioning in a shorter period.

8.5.2 Removing the Virus

Once you have isolated the infected machine or machines, the next step is to clean them. If you know the specific virus, then you should be able to remove it by running an antivirus program, or you should be able to find virus removal instructions on the Internet. In the highly unlikely event that you cannot remove the virus, then you may have no other choice but to format the machine (or machines) and restore them from backups. However, it must be stressed that such a situation is very unlikely.

If you do successfully remove the virus, you will want to scan the machine thoroughly for any other virus infections before reconnecting it to your network. You should be certain it is completely clean before putting it back online.

8.5.3 Finding how the Infection Started

Once you have contained and removed the virus, the next goal is to see that it does not reappear. This is done by finding out how the virus got onto your system in the first place. To do this, you need to investigate the situation in three ways:

  • Talk to users of the infected machines and see if anyone opened any e-mail attachments, downloaded anything, or installed anything. Since these are the three most likely avenues for virus infection, they should be checked first.
  • Read any online documentation for that specific virus. It will tell you the normal method of propagation.
  • If neither of those avenues tells you what occurred, check any activity

8.6 Trojan Horses

A Trojan horse is an application that appears to have a benign purpose but actually performs some malicious function. This deception is what makes these applications a dangerous threat to your system. The Internet is full of useful utilities (including many security tools), screen savers, images, and documents. Most Internet users do download some of these things. Creating an attractive download that has a malicious payload is an effective way of gaining access to a person’s computer.

One defence against Trojan horses is to prevent all downloads, but that is not particularly practical. The value of the Internet is the easy access it provides to such a wide variety of information—restricting that access in such a draconian manner disrupts one of the most important reasons for giving employees Internet access. Instead of using such a heavy-handed tactic, you will learn other ways to protect your systems from Trojan horses.

Once you have a Trojan horse on your system, it may perform any number of unwanted activities. Some of the most common actions Trojan horses take include:

  • Erasing files on a computer.
  • Spreading other malware, such as viruses. Another term for a Trojan horse that does this is a dropper.
  • Using the host computer to launch distributed denial of service (DDoS) attacks or send spam.
  • Searching for personal information such as bank account data.
  • Installing a back door on a computer system. This means providing the creator of the Trojan horse easy access to the system, such as creating a username and password she can use to access the system.

Of the items on the above list, installing back doors and executing distributed denial of service attacks are probably the most frequent results of a Trojan horse attack, though installing spyware and dropping viruses are becoming much more common as well.

Below there is a list with some famous Trojan Horses:

  • Back Orifice
  • Anti-Spyware 2011
  • Shedun
  • Brain Test
  • FinFisher
  • NetBus
  • FlashBack

8.6.1 Trojan Horses Symptoms

It is difficult to determine whether your system is victim of a Trojan horse. There are a number of symptoms that might indicate that you have a Trojan horse. Assuming, of course, that you or another legitimate user are not making these changes, such symptoms include:

  • Home page for your browser changing
  • Any change to passwords, usernames, accounts, etc.
  • Any changes to screen savers, mouse settings, backgrounds, etc.
  • Any device (such as a CD door) seeming to work on its own

Any of these changes are symptoms of a Trojan horse and indicate your system is probably infected.

8.7 Spyware or Adware

Spyware is a growing problem both for home computer users and for organisations. There is, of course, the risk that such applications might compromise some sensitive information. Another problem of such applications is that they consume too much of your system’s resources. Spyware and adware both use memory. If your system has too many such applications, then they can consume so much of your system’s resources that your legitimate software will have trouble running.

The primary difference between spyware and adware is what they do on your machine. They both infect your machine in the same manner. Spyware seeks to get information from your machine and make it available to some other person. This can be done in a number of ways. Adware seeks to create pop-up ads on your machine. Because these ads are not generated by the web browser, many traditional pop-up blockers will not stop them.

Both spyware and adware are growing problems for network security and home PC security. This is an important element of computer security software that was at one time largely ignored. Even today, not enough people take spyware seriously enough to guard against it. Some of these applications simply change your home page to a different site (these are known as home page hijackers); others add items to your favourites (or read items from them). Other applications can be even more intrusive.

Below there is a list with some famous spyware and adware:

  • Gator
  • RedSheriff

8.7.1 Anti-Spyware

Most antivirus products include anti-spyware. However, you can purchase dedicated anti-spyware software. Anti-spyware is an excellent way to defend against spyware and adware, just as antivirus software defends against viruses and Trojan horses. Essentially, it is software that scans your computer to check for spyware running on your machine. Most anti-spyware works by checking your system for known spyware files. It is difficult to identify specific activities that identify spyware, as you can with viruses. Each application must simply be checked against a list of known spyware. This means that you must maintain some sort of subscription service so that you can obtain routine updates to your spyware definition list.

In today’s Internet, running anti-spyware is as essential as running antivirus software. Failing to do so can lead to serious consequences. Personal data and perhaps sensitive business data can easily leak out of your organisation without your knowledge due to spyware. You should also keep in mind that it is entirely possible for spyware to be the vehicle for purposeful industrial espionage.



9.1 User Policies Definition

Misuse of systems is a major problem for many organisations. A large part of the problem comes from the difficulty in defining what exactly misuse is. Some things might be obvious misuse, such as using company time and computers to search for another job or to view forbidden websites.

However, other areas are not so clear, such as an employee using her lunchtime to look up information about a car she is thinking of buying. Generally, good user policies outline specifically how people may use systems and how they may not. For a policy to be effective, it needs to be very clear and quite specific. Statements such as “computers and Internet access are only for business use” are simply inadequate.

Every organisation must have specific policies that will be applied fairly across the organisation. In the previous example, using a general statement of “computers and Internet access are only for business use” can be problematic. Assume you have an employee who occasionally takes just a few minutes to check home e-mail with the company computer. You decide that this is acceptable, and choose not to apply the policy. Later another employee spends two to three hours per day surfing the Net and you fire him for violating company policy. That employee might sue the company for wrongful termination.

Other areas for potential misuse are also covered by user policies, including password sharing, copying data, leaving accounts logged on while employees go to lunch, and so on. All of these issues ultimately have a significant impact on your network’s security and must be clearly spelled out in your user policies. We will now examine several areas that effective user policies must cover:

  • Passwords
  • Internet use
  • E-mail attachments
  • Software installation and removal
  • Instant messaging
  • Desktop configuration
  • BYOD

9.1.1 Passwords

Keeping passwords secure is critical. Appropriate passwords are part of operating system hardening. You should recall that a good password has in the past been defined as one that is six to eight characters long, uses numbers and special characters, and has no obvious relevance to the end user. For example, a user will use a password like “cowboys” or “godallas,” but it should be advised to use a password like “%trEe987” or “123DoG$$” because those do not reflect the person’s personal interests and therefore will not be easily guessed.

Issues such as minimum password length, password history, and password complexity come under administrative policies, not user policies. Those complexity requirements are still good recommendations. However, you should consider longer passwords, such as those 12 characters or longer. User policies dictate how the end user should behave.

However, no password is secure, no matter how long or how complex, if it is listed on a Post-it note stuck to the user’s computer monitor. This may seem obvious, but it is not at all uncommon to go into an office and find a password either on the monitor or in the top drawer of the desk. Every janitor or anyone who simply passes by the office can get that password.

It is also common to find employees sharing passwords. For example, Bob is going to be out of town next week, so he gives Alice his password so that Alice can get into his system, check e-mail, and so on. The problem is that now two people have that password. And what happens if, during the week Bob is gone, Alice gets ill and decides she will share the password with Shelly so she can keep checking that system while Alice is out sick? It does not take long for a password to get to so many people that it is no longer useful at all from a security perspective.

Issues like minimum length of passwords, password age, password history are issues of administrative policies. System administrators can force these requirements. However, none of that will be particularly helpful if the users do not manage their passwords in a secure fashion.

All of this means you need explicit policies regarding how users secure their passwords. Those policies should specify:

  • Passwords are never to be kept written down in any accessible place. The preference is that they not be written down at all, but if they are, they should be in a secure area such as a lock box.
  • Passwords must never be shared with any person for any reason.
  • If an employee believes his password has been compromised, he should immediately contact the IT department so that his password can be changed and so that logon attempts with the old password can be monitored and traced.

A recommendation is to choose a passphrase, something like ILikeCheeseBurgers, and then change the e’s to 3’s and use some capitalization. Perhaps add a symbol so it becomes #ILik3Ch33s3Burg3rs. This is a very secure password. It can be remembered and it has complexity and length.

The complexity requirements prevent dictionary attacks (using words from a dictionary) and guessing. However, you might be wondering why a long password is so important. The reason has to do with how passwords are stored. In Windows when you select a password, that password is stored in hashed format in a SAM file. Remember that a hash cannot be undone. Therefore, when you log in, Windows will hash whatever you type in and compare it to what’s in the SAM file. If they match, you are in.

Hashing passwords leads to the use of an interesting hacking technique called the rainbow table. A rainbow table contains all the possible hashes of all the key combinations that might have been used in a password, up to a given size. For example, all the single-character combinations are hashed, all the two-character combinations are hashed, and so on up to some finite limit (often 8 to 10 characters). If you get the SAM file then you can search the rainbow table for any matches. If you find a match, then the associated plaintext must be the password. Tools such as OphCrack boot into Linux and then run a rainbow table against the SAM file. However, larger rainbow tables are cumbersome. No current rainbow tables can handle passphrases of 20 characters or more.

9.1.2 Internet use Policy

Most organisations provide users with some sort of Internet access. There are several reasons for this. The most obvious reason is e-mail. However, that is hardly the only reason to have Internet access in a business. There is also the web, and even chat rooms. All of these can be used for legitimate purposes within any organisation but can also be serious security problems. Appropriate polices must be in place to govern the use of these technologies.

The web is a wonderful resource for a tremendous wealth of data. The Internet is also full with useful tutorials on various technologies. However, even nontechnology-related business interests can be served via the web. Here are a few examples of legitimate business uses of the web:

  • Sales staff checking competitors websites to see what products or services they offer in what areas, perhaps even getting prices
  • Creditors checking a business’s AM Best or Standard and Poor’s rating to see how their business financial rating is doing
  • Business travellers checking weather conditions and getting prices for travel

Of course, other web activities are clearly not appropriate on a company’s network:

  • Using the web to search for a new job
  • Any pornographic use
  • Any use which violates local, state, or federal laws
  • Use of the web to conduct employee’s own business (i.e., an employee who is involved in another enterprise other than the company’s business, such as eBay)

In addition, there are grey areas. Some activities might be acceptable to some organisations but not to others. Such activities might include:

  • Online shopping during the employee’s lunch or break time
  • Reading news articles online during lunch or break time
  • Viewing humorous websites

What one person might view as absurdly obvious might not be to another. It is critical that any organisation have very clear policies detailing specifically what is and what is not acceptable use of the web at work. Giving clear examples of what is acceptable use and what is not is important. You should also remember that most proxy servers and many firewalls could block certain websites. This will help prevent employees from misusing the company’s web connection.

9.1.3 Email Attachments

Most business and even academic activity now occurs via e-mail. As we have discussed in several previous chapters, e-mail also happens to be the primary vehicle for virus distribution. This means that e-mail security is a significant issue for any network administrator.

Clearly you cannot simply ban all e-mail attachments. However, you can establish some guidelines for how to handle e-mail attachments. Users should open an attachment only if it meets the following criteria:

  • It was expected (i.e., the user requested documents from some colleague or client).
  • If it was not expected, it comes from a known source. If so, first contact that person and ask whether they sent the attachment. If so, open it.
  • It appears to be a legitimate business document (that is, a spread sheet, a document, a presentation, etc.).

It should be noted that some people might find such criteria unrealistic. There is no question they are inconvenient. However, with the prevalence of viruses, often attached to e-mail, these measures are sensible. Many people choose not to go to this level to try to avoid viruses, and that may be your choice as well. Just bear in mind that millions of computers are infected with some sort of virus every single year.

No one should ever open an attachment that meets any of the following criteria:

  • It comes from an unknown source.
  • It is some active code or executable.
  • It is an animation/movie.
  • The e-mail itself does not appear legitimate. (It seems to tempt you to open the attachment rather than simply being a legitimate business communication that happens to have an attachment.)

If the end user has any doubt whatsoever, then should not open the e-mail. Rather, should contact someone in the IT department who has been designated to handle security. That person can then either compare the e-mail subject line to known viruses or can simply come check out the e-mail personally. Then if it appears legitimate, the user can open the attachment.

9.1.4 Software Installation and Removal


This is one matter that does have an absolute answer. End users should not be allowed to install anything on their machine, including wall papers, screen savers, utilities etc. The best approach is to limit their administrative privileges so they cannot install anything. However, this should be coupled with a strong policy statement prohibiting the installation of anything on users’ PCs. If they wish to install something, it should first be scanned by the IT department and approved.

This process might be cumbersome, but it is necessary. Some organisations go so far as to remove media drives (optical drive, USB, etc.) from end users’ PCs so installations can occur only from files that the IT department has put on a network drive. This is usually a more extreme measure than most organisations will require, but it is an option you should be aware of.

9.1.5 Instant Messaging

Instant messaging is also widely used and abused by employees in companies and organisations. In some cases, instant messaging can be used for legitimate business purposes. However, it does pose a significant security risk. There have been viruses that propagated specifically via instant messaging. In one incident the virus would copy everyone on the user’s buddy list with the contents of all conversations. Thus, a conversation the user thought was private was being broadcast to everyone with whom that user had messaged.

Instant messaging is also a threat from a purely informational security perspective. Without the traceability of an e-mail going through the corporate e-mail server, nothing stops an end user from instant messaging out trade secrets or other confidential information undetected. It is recommended that instant messaging simply be banned from all computers within an organisation. If you find your organisation absolutely must use it, then you must establish very strict guidelines for its use, including:

  • Instant messaging may be used only for business communications, no personal conversations. Now this might be a bit difficult to enforce. More common rules, such as prohibiting personal web browsing, are also quite difficult to enforce. However, it is still a good idea to have those rules in place. Then if you find an employee violating them, you can refer to a company policy that prohibits such actions. However, you should be aware that in all likelihood you would not catch most violations of this rule.
  • No confidential or private business information should be sent via instant messaging.

9.1.6 Desktop Configuration

Many users like to reconfigure their desktop. This means changing the background, screen saver, font size, resolution, and so on. Theoretically speaking, this should not be a security hazard. Simply changing a computer’s background image cannot compromise the computer’s security. However there are other issues involved.

The first issue is where the background image comes from. Frequently end users download images from the Internet, creating an opportunity for getting a virus or Trojan horse, particularly one using a hidden extension (e.g., it appears to be a mypic.jpg but is really mypic.jpg.exe). There are also human resources/harassment issues if an employee uses a backdrop or screen saver that is offensive to other employees. Some organisations simply decide to prohibit any changes to the system configuration for this reason.

The second problem is technical. In order to give a user access to change screen savers, background images, and resolution, you must give rights that also allow to change other system settings you might not want changed. The graphical display options are not separated from all other configuration options. This means that allowing the user to change screen saver might open the door to alter other settings that would compromise security (such as the network card configuration or the Windows Internet connection firewall).

9.1.7 Bring Your Own Device (BYOD)

Bring Your Own Device (BYOD) has become a significant issue for most organisations. Most, if not all, of your employees will have their own smart phones, tablets, smart watches, etc. that they will most likely carry with them into the workplace. When they connect to your wireless network, this introduces a host of new security concerns. You have no idea what networks those devices previously connected to, what software was installed on them, or what data might be exfiltrated by these personal devices.

In highly secure environments, the answer may be to forbid personally owned devices. However, in many organisations, such a policy is impractical. A workaround for that is to have a Wi-Fi network that is dedicated to BYOD and is not connected to the company’s main network. Another approach, although more technologically complex, is to detect the device on connection, and if it is not a company-issued device, significantly limit its access.

There are also alternatives to BYOD. For example, Choose Your Own Device (CYOD) is a policy wherein the company allows the employee to bring their own device, but only if that device is from a list of pre-approved devices. This gives the company some control over what the user is connecting to the company network.

COPE, or Company Owned and Provided Equipment, is another option. In this scenario, the company provides the device, and has complete control over it. However, this can become an issue when the employee uses a device for both personal and professional purposes, not to mention the expense of providing employees with devices and maintaining those devices.

Whatever approach you take, you must have some policy regarding personal devices. They are already ubiquitous and spreading even more. Just a few years ago, smart phones were really the only BYOD device. But today there are smart watches, smart luggage, etc., and it is difficult to predict what new devices might be coming in the future.


9.2 Guided Exercise: Analysing Policies

Files None
Machines Windows 10

In this exercise you will use the PolicyAnalyser tool to analyse existing policies and provide recommendations.

Login to Windows 10 and open the Desktop folder Exercises -> PolicyAnalyzer.  

Double click the file PolicyAnalyzer to start it. Click run on the Security Warning window. 

Check the box Local Policy and then click on View/Comapre button. Click Yes on the User Account Control Window and click Run on the Security Warning window.

Once the results are shown scroll till you find the Policy Setting for SAM. The Local policy says No Autiding. What will be your recommendation? 

A recommendation will be to audit such object as the SAM file contains the password hashes for the Windows users.

Guided Exercise Video




9.3 System Administration Policies

In addition to determining policies for users, you must have some defined policies for system administrators. There must be a procedure for adding users, removing users, dealing with security issues, changing any system, and so on. There must also be procedures for handling any deviation.

9.3.1 New Employees

When a new employee is hired, the system administration policy must define specific steps to safeguard company security. New employees must be given access to the resources and applications their job functions require. The granting of that access must be documented (possibly in a log). It is also critical that each new employee receive a copy of the company’s computer security/acceptable use policies and sign a document acknowledging receipt of such.

Before a new employee starts to work, the IT department (specifically network administration) should receive a written request from the business unit for which that person will be working. That request should specify exactly what resources this user will need and when will start. It should also have the signature of someone in the business unit with authority to approve such a request. Then, the person who is managing network administration or network security should approve and sign the request. After you have implemented the new user on the system with the appropriate rights, you can file a copy of the request.

9.3.2 Leaving Employees

When an employee leaves, it is critical to make sure all logins are terminated and all access to all systems is discontinued immediately. Unfortunately, this is an area of security that many organisations do not give enough attention to. It is imperative to have all of the former employee’s access shut down on his last day of work. This includes physical access to the building. If a former employee has keys and is displeased, nothing can stop him from returning to steal or vandalize computer equipment. When an employee leaves the company, you should ensure that on his last day the following actions take place:

  • All logon accounts to any server, VPN, network, or other resources are disabled.
  • All keys to the facility are returned.
  • All accounts for e-mail, Internet access, wireless Internet, cell phones, etc., are shut off.
  • Any accounts for mainframe resources are cancelled.
  • The employee’s workstation hard drive is searched.

The last item might seem odd. However, if an employee was gathering data to take with him (proprietary company data) or conducting any other improper activities, you need to find out right away. If you do see any evidence of any such activity, you need to secure that workstation and keep it for evidence in any civil or criminal proceedings.

All of this might seem a bit extreme for some people. It is true that with the vast majority of exiting employees, you will have no issues of concern. However, if you do not make it a habit of securing an employee’s access when he departs, you will eventually have an unfortunate situation that could have been easily avoided.

9.3.3 Change Requests

The nature of IT is change. Not only end users come and go, but requirements change frequently. Business units request access to different resources, server administrators upgrade software and hardware, application developers install new software, web developers change the website, and so on. Change is occurring all of the time. Therefore, it is important to have a change control process. This process not only makes the change run smoothly but also allows the IT security personnel to examine the change for any potential security problems before it is implemented. A change control request should go through the following steps:

  • An appropriate manager within the business unit signs the request, signifying approval.
  • The appropriate IT unit (database administration, network administrator, e-mail administrator, and so on) verifies that the request is one they can fulfil (from both a technological and a budgetary/business perspective).
  • The IT security unit verifies that this change will not cause any security problems.
  • The appropriate IT unit formulates a plan to implement the change and a plan to roll back the change in the event of some failure.
  • The date and time for the change is scheduled, and all relevant parties are notified.

Your change control process might not be identical to this one; in fact, yours might be much more specific. However, the key to remember is that in order for your network to be secure, you simply cannot have changes happening without some process for examining their impact prior to implementing them.

9.4 Access Control

An important area of security policies that usually generates some controversy in any organisation is access control. There is always a conflict between users’ desire for unrestricted access to any data or resources on the network and the security administrator’s desire to protect that data and resources. You cannot simply lock down every resource as completely as possible because that would block the users’ access to those resources. Conversely, you cannot simply allow anyone and everyone complete access to everything.

It is worth keeping this acronym in mind when thinking about access control. Your goal is to make sure the data is accurate, confidential, and available only to authorised parties.

This is where the least privileges concept comes into play. The idea is simple. Each user, including IT personnel, gets the least access they can have to effectively do the job. Rather than asking the question “Why not give this person access to X?” you should ask “Why give this person access to X?” If you do not have a very good reason, then do not provide the access. This is one of the fundamentals of computer security. The more people who have access to any resource, the more likely some breach of security is to occur.

Clearly trade-offs between access and security must be made. One common example involves sales contact information. Clearly, a company’s marketing department needs access to this data. However, what happens if competitors get all of your company’s contact information? That information could allow them to begin targeting your current client list. This requires a trade-off between security and access. In this case, you would probably give sales people access only to the contacts that are within their territory. No one other than the sales manager should have complete access to all contacts.

10.1 Risk Assessment

Evaluating the security of a network always starts with a risk assessment. This involves considering the assets you are trying to protect, the threats against those assets, vulnerabilities in your systems, and what measures you can take to protect them. There are formulas for calculating risk.

The most basic calculation is for a single loss expectancy (SLE), or what impact a single loss will cause. This is calculated by multiplying the asset value (AV) by the exposure factor (EF). The exposure factor is a percentage value, representing how much of the asset’s value you will lose in a given incident. For example, a laptop that has depreciated by 20 percent is now only worth 80 percent of its original value, should it be lost or stolen. This formula is


Therefore, if a laptop is purchased for $800, and depreciates by 10 percent a year, thus yielding an exposure factor of .9 (90 percent), then the SLE for a stolen or lost laptop is

SLE = 800 (AV) × .9 (EF)
SLE = $720

The next formula is the annualized loss expectancy (ALE). This represents how much loss you can expect from a particular issue in a year. The formula is SLE multiplied by annual rate of occurrence (ARO):


So, in the previous laptop example, if you think you will lose six laptops per year, the calculation is

ALE = 720 (SLE) × 6 (ARO)
ALE = $4320

As you can see, the math is actually quite simple. Another concept to understand is residual risk. Basically, this is how much risk is left over after you have taken all the steps you can to deal with the risk. In addition, that topic brings us to the issue of how you deal with a risk you have identified. There are really only four categories of responses:

  • Mitigation: This means you take steps to lessen the risk. No matter what you do, there is likely to be some risk left. For example, if you are concerned about malware, then running antivirus is risk mitigation. This is the most common solution.
  • Avoidance: This is difficult to do. It means you have zero risk. For example, if you are concerned about users downloading a virus from a website, the only way to completely avoid that is to not give them access to the web. This is not usually a viable solution.
  • Transference: This is transferring the risk to someone else. The clearest example is cyber breach insurance. If you have such insurance, then the cost of a risk that is realized will be passed on to the insurance company.
  • Acceptance: If the probability of the risk is very remote, or the cost of mitigation is higher than the cost of the risk being realized, you may choose to do nothing, and simply accept the risk.



10.2 Conducting an Initial Assessment

Disaster recovery, access rights, and appropriate policies are topics that are often overlooked by those new to security. To keep it simple and easy to remember, the stages of assessing a system’s security can be separated into the “Six Ps”:

  • Patch
  • Ports
  • Protect
  • Policies
  • Probe
  • Physical

You should note that these Six Ps are not yet standards in the security industry. They are provided here as a framework for approaching system security.

10.2.1 Patches


Patching a system is perhaps the most fundamental part of security. Therefore, when assessing any system’s security, you should check to see whether a procedure is in place to govern the routine updating of all patches. And you should also, of course, check to see that the machines actually have current patches and updates. A written policy is essential, but when performing a security audit, you need to ensure that those policies are actually being followed.

As you are aware, operating system and application vendors occasionally discover security flaws in their products and release patches to correct these flaws. Unfortunately, it is not uncommon to find organisations in which patches have not been applied as late as 30 days or more after their release.

10.2.2 Ports

All communication takes place via some port (TCP/UDP). This is also true for many virus attacks. Frequently virus attacks will utilize some uncommon port to gain access to your system. Recall that ports 1 through 1024 are assigned and used for well-known protocols. We have examined viruses, Trojan horses, and other dangers that operate on specific port numbers. If those ports are closed, then your vulnerability to these specific attacks is significantly reduced.

Unfortunately, some system administrators do not make a policy of closing unused ports. This is probably due to the fact that many administrators think that if the firewall is blocking certain traffic, then there is no need to block that port on individual machines. However, this approach provides you with only perimeter security, not layered security. By closing ports on individual machines, you provide a backup in case the firewall is breached.

As a rule, any port you do not explicitly need for operations should be closed, and communication should be disallowed on this port. A port is usually associated with a service. For example, an FTP service is often associated with ports 21 and 20. In order to close a port on an individual machine, you would need to shut down the service that uses that port. This means those unused services on servers and individual workstations should be shut down.

Both Windows and Linux have built-in firewall capability that will block certain ports. This means in addition to shutting down the particular unneeded services on all client machines, you should also shut down the ports.

You should also shut down any unused router ports in your network. If your network is part of a larger wide-area network (WAN), then it is likely you have a router connecting you to that WAN. Every open port is a possible avenue of entry for a virus or intruder. Therefore, every port you can close is one less opportunity for such attacks to affect your system.

The specifics of how to close a port on a router are particular to the individual router. The documentation that came with your router or your vendor should be able to provide you with specific instructions for how to accomplish this. If you have a vendor servicing your router, then you should make a list of all required ports and request that the vendor close all other ports on the router.

10.2.3 Protect

The next phase is to ensure that all reasonable protective software and devices are employed. This means at a minimum having a firewall between your network and the outside world. Clearly, more advanced firewalls such as stateful packet inspection firewalls are preferred. When auditing a system, you must note not only whether the system has a firewall, but also what type of firewall it has. You should also consider using an intrusion detection system (IDS) on that firewall and any web servers.

However, IDSs are the only way to know of imminent attacks, and there are free, open source IDSs available. For that reason, most experts highly recommend them. The firewall and IDS will provide basic security to your network’s perimeter, but you also need virus scanning. Each and every machine, including servers, must have a virus scanner that is updated regularly. The point has already been made that a virus infection is the greatest threat to most networks. As also previously discussed, it is probably prudent to consider anti-spyware software on all of your systems. This will prevent users of your network from inadvertently running spyware on the network.

Finally, a proxy server is a very good idea. It not only masks your internal IP addresses, but most proxy servers allow you to discover what websites users visit and put on filters for certain sites. Many security experts consider a proxy server to be as essential as a firewall.

In addition to protecting your network, you must also protect data that is transmitted, particularly outside your network. All external connections should be made via a VPN. Having data encrypted prevents hackers from intercepting the data via a packet sniffer. For more secure locations, you might even look for all internal transmissions to be encrypted as well.

In short, when assessing the protection of the network, check to see whether the following items are present, properly configured, and functioning:

  • Firewall
  • Antivirus protection
  • Anti-spyware protection
  • IDS
  • Proxy server or NAT
  • Data transmissions encryption

Be aware that the first two items are met in most networks. Any network that does not have a firewall or antivirus software is so substandard that the audit should probably stop at that point. In fact, it is unlikely that such an organisation would even bother to have a security audit. The IDS and data encryption options are probably less common; however, they should be considered for all systems.

10.2.4 Physical

In addition to securing your network from unwanted digital access, you must also ensure that it has adequate physical security. The most robustly secure computer that is left sitting unattended in an unlocked room is not at all secure. You must have some policy or procedure governing the locking of rooms with computers as well as the handling of laptops, tablets, and other mobile computer devices. Servers must be in a locked and secure room with as few people as is reasonably possible having access to them. Backup tapes should be stored in a fireproof safe. Documents and old backup tapes should be destroyed before disposal (e.g., by melting tapes, de-magnetizing hard disks, breaking CDs).

Physical access to routers and switches should also be tightly controlled. Having the most high-tech, professional information security on the planet but leaving your server in an unlocked room to which everyone has access is a recipe for disaster. One of the most common mistakes in the arena of physical security is co-locating a router or switch in a janitorial closet. This means that, in addition to your own security personnel and network administrators, the entire cleaning staff has access to your router or switch, and any one of them could leave the door unlocked for an extended period of time.

There are some basic rules you should follow regarding physical security:

  • Server rooms: The room where servers are kept should be the most fire-resistant room in your building. It should have a strong door with a strong lock, such as a deadbolt. Only those personnel who actually have a need to go in the room should have a key. You might also consider a server room log wherein each person logs in when they enter or exit the room. There are actually electronic locks that record who enters a room, when they enter, and when they leave. Consult local security vendors in your area for more details on price and availability.
  • Workstations: All workstations should have an engraved identifying mark. You should also routinely inventory them. It is usually physically impossible to secure them as well as you secure servers, but you can take a few steps to improve their security.
  • Miscellaneous equipment: Projectors, CD burners, laptops, and so forth should be kept under lock and key. Any employee that wishes to use one should be required to sign it out, and it should be checked to see that it is in proper working condition and that all parts are present when it is returned.

These measures should be considered by all organisations. Some organisations go much further in ensuring physical security, and we will list some of the more extreme measures here. Most are probably more extreme than businesses require. However, if you deal with highly sensitive or classified data, then you might want to consider some or all of these measures.

  • Biometric locks to all server rooms, or equipment storage rooms. Such locks are triggered by a fingerprint scan, and the identity of the person as well as the time they entered the room are recorded.
  • All visitors to the building are logged in (both their entry and exit time) and are escorted by an employee at all times.
  • All bags are inspected when personnel leave, or at least some bags are inspected at random.
  • No portable devices that might record data are allowed on the premises. This includes USB drives, camera phones, or any device that might copy data or record screen images.
  • All printing is logged. Who printed, the time the printing occurred, the document name, and the document size.
  • All copying is logged, similarly to printing.

If you are in a situation that demands a greater than normal security level, these measures may be considered.

10.3 Probing the Network

Perhaps the most critical step in assessing any network is to probe the network for vulnerabilities. This means using various utilities to scan your network for vulnerabilities. Some network administrators skip this step. They audit policies, check the firewall logs, check patches, and so on. However, the probing tools discussed in this section are the same ones that most hackers use.

If you want to know how vulnerable your network is, it is sensible to try the same tools that an intruder would use. In this section, we review the common scanning/probing tools. There are essentially three types of probes that are usually done. These are the same types of probes that skilled hackers use to evaluate your network:

  • Port scanning: This is a process of scanning the well-known ports (there are 1024) or even all the ports (there are 65,535) and seeing which ports are open. Knowing what ports are open tells a lot about a system. If you see that 160 and 161 are open that tells you that the system is using SNMP. From the perspective of a network administrator, there should be no ports open that are not necessary.
  • Enumeration: This is a process whereby the attacker tries to find out what is on the target network. Items such as user accounts, shared folders, printers, and so on are sought after. Any of these might provide a point of attack.
  • Vulnerability assessment: This is the use of some tool to seek out known vulnerabilities, or the attacker might try to manually assess vulnerabilities. Some outstanding tools are available for vulnerability assessment.

A number of tools are freely available on the Internet for active scanning. They range from the simple to complex. Anyone involved in preventing or investigating computer crimes should be familiar with a few of these. The most famous vulnerability scanners are Nessus, Qualys, Openvas, Netsparker, Acunetix, Nexpose Community, Retina and Core Impact.

10.4 Guided Exercise: Probing the Network

Files None
Machines Ubuntu Server, Windows Server, Windows 10

In this exercise you will use a tool called Nmap to scan and identify open ports on the Windows Server and Windows 10.

Login to Ubuntu Server. Once logged in run the command nmap to find which ports are open on Windows Server.

Determine the actual service running on each port by running the command “nmap –sV”

Run the command nmap to identify the open ports on the Windows 10 machine. 

Run the command nmap –sV to identify theactual service running on the open ports.

Guided Exercise Video

10.5 Vulnerabilities

It is important to understand precisely what a vulnerability is. A vulnerability is some flaw in a system that an attacker could exploit to attack the system.

10.5.1 CVE

The most common list of vulnerabilities is the CVE list. Common Vulnerabilities and Exposures (CVE) is a list maintained by the Mitre Corporation at It is not only the most common, but also the most comprehensive vulnerability list. The CVE list was designed to provide a common name and description for a vulnerability. This allows security professionals to communicate effectively about vulnerabilities. In the past, CVEs had been designated by a CVE ID in the format of CVE-YYYY-NNNN. This format only allows 9,999 unique identifiers per year. The new format is CVE prefix + Year + Arbitrary Digits and allows for any number of digits.

10.5.2 NIST

The U.S. National Institute of Standards and Technology maintains a database of vulnerabilities that you can access at NIST also uses the CVE format. For example, CVE-2017-12371 is described as “A ‘Cisco WebEx Network Recording Player Remote Code Execution Vulnerability’ exists in Cisco WebEx Network Recording Player for Advanced Recording Format (ARF) and WebEx Recording Format (WRF) files. A remote attacker could exploit this by providing a user with a malicious ARF or WRF file via email or URL and convincing the user to launch the file. Exploitation of this could cause an affected player to crash and, in some cases, could allow arbitrary code execution on the system of a targeted user.”

10.5.3 OWASP

The Open Web Application Security Project is the standard for web application security. They publish a number of important documents. For our current purposes, the most important is their top 10 list, located at Every few years they publish a top 10 web application vulnerabilities list. This list contains the actual vulnerabilities most frequently found in web applications.

10.6 Guided Exercise: Learning about Vulnerabilities

Files None
Machines None

In this exercise you will identify details regarding a specific vulnerability. You will need to use a web browser for this exercise not in the lab environment.

Open a web browser and type the following link

From the menu click on Search CVE List. In the search box enter CVE-2019-0708 and click on Submit.

One entrie will be returned and click on it to learn more about that specific vulnerabilitiry.Read the description carefully and you will note that the vulnerability affects the Remote Desktop Services on Windows machines.

Guided Exercise Video


10.7 Documenting Security

By this point, you are undoubtedly aware that you need to document your security. However, you may not be clear as to exactly what documents you should have. Unfortunately, this is an area of network security for which there are not industry standards. There is no manual on documentation.

10.7.1 Physical Security Documentation

You should have a document that lists physical security that is in place. Where are the machines located? This means documenting the location of every single server, workstation, router, hub, or other device. The documentation should contain serial numbers as well as what personnel have access to them. If a device is in a locked room, then the documentation should also have a list of who has keys to that room.

If you log entry to secured rooms, then copies of those logs should be filed with your other physical documentation. In even a medium-sized network, this would quickly become a rather hefty file rather than a single document. You may consider implementing some method whereby after a certain period of time (1 year, for example) the access logs are archived, then after a longer period of time (such as 3 years) they are destroyed.

10.7.2 Policy and Personnel Documentation

All policies must be on file. Any revisions should be filed along with the originals. Assuming you have employees sign an agreement stating they are aware of the policies (and you absolutely should), then copies of that should also be on file.

Along with policy documentation, you should keep a list of personnel along with what items they have access to. This includes physical access as well as any machines (servers, workstations, or routers) that they have login rights. You should also note what level of access they have (standard user, power user, administrator, and so on).

10.7.3 Probe Documents

Any time you conduct any security audit, a report of that audit should be filed. Even audits done by outside consultants should be kept on file. The audit report should include any flaws found, and have a follow-up report of what steps were taken to correct them.

Should you have a security incident (such as a virus infection or intruder), there should be at least a brief memo summarizing what occurred. That document should state what the security incident was, when it occurred, what machines were affected, and how it was corrected.

10.7.4 Network Protections Documents

The most obvious item to document is exactly what network protections you have in place. This documentation should detail the following:

  • What firewall are you using and how is configured.
  • What IDS are you using and how is configured.
  • What antivirus and/or anti-spyware you are using.
  • Have you configured any honeypots?
  • What individual machine security measures (such as workstation firewalls) have you taken?

One note of caution: These documents should be kept under lock and key, with only limited access. If an intruder were to get access to these documents, they would have a detailed analysis of your network’s weaknesses.

One thought on “Network Security -4

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