Defining a Computer Virus

The information technology market has many threats with one of the main threats being viruses and worms. Worms and viruses have been known as one of the hackers’ best tools to steal information from unsuspecting persons of interest.

Think of a biological virus – the kind that makes you sick. It is persistently nasty, keeps you from functioning normally and often requires something powerful to get rid of it. A computer virus is very similar. Designed to replicate relentlessly, computer viruses infect your programs and files, alter the way your computer operates or stop it from working altogether. It is estimated that the Conficker virus infected more than 10 million computers in 2009. Tens of thousands of computer viruses now operate over the Internet, and new computer viruses are discovered every day.

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The internet is the ideal hub for computer viruses where unsuspecting users become daily victims. The following are some subclasses of worms and viruses;

Classifications of Worms

  • Email-Worm
  • IM-Worm
  • IRC-Worm
  • Net-Worm
  • P2P-Worm

Classifications of Viruses

1. Macro Viruses

These viruses infect the files created using some applications or programs that contain macros such as doc, ppt, xls and mdb. They automatically infect the files with macros and also templates and documents that are contained in the file. They hide in documents shared through e-mail and networks.

Macro viruses include:

  • Relax
  • Bablas
  • Melissa.A
  • 097M/Y2K

2.Memory Resident Viruses

They usually fix themselves inside the computer memory. They are activated every time the OS runs and end up infecting other opened files. They hide in RAM.

Memory Resident Viruses Include:

  • CMJ
  • meve
  • randex
  • MRK lunky

3.Overwrite Viruses

These types of viruses delete any information in a file they infect, leaving them partially or completely useless once they are infected. Once in the computer, they replace all the file content but the file size does not change.

Overwrite Viruses Include:

  • Trj.Reboot
  • way
  • trivial.88.D

4.Direct Action Viruses

These viruses mainly replicate or take action once they are executed. When a particular condition is met, the viruses will act by infecting the files in the directory or the folder specified in the AUTOEXEC.BAT. The viruses are generally found in the hard disk’s root directory, but they keep on changing location.

Direct Action Viruses Include:

  • Vienna virus

5.Directory Virus

Also known as cluster virus or file system virus. They infect the computer’s directory by changing the path indicating file location. They are usually located on the disk but affect the entire directory.

Directory Viruses Include:

  • dir-2 virus

6.Web Scripting Virus

Most web pages include some complex codes in order to create an interactive and interesting content. Such a code is often exploited to cause certain undesirable actions. They mostly originate from the infected web pages or browsers.

Web Scripting Viruses Include:

  • JS.Fortnight – a virus that spreads via malicious emails.

7.Multipartite Virus

These type of viruses spread in many different ways. Their actions vary depending on the OS installed and the presence of certain files. They tend to hide in the computer’s memory but do not infect the hard disk.

Multipartite Viruses Include:

8.FAT Viruses

These lardy viruses attack the file allocation table (FAT) which is the disc part used to store every information about the available space, location of files, unusable space, etc.

FAT Viruses Include:

  • the link virus

9.Companion Viruses

These types of viruses infect files just like the direct action and the resident types. Once inside the computer, they ‘accompany’ other existing files.

Companion Viruses Include:

  • Asimov.1539
  • stator and terrax.1069

10.Polymorphic Virus

They encode or encrypt themselves in a different way every time they infect your computer. They use different encryption and algorithms. This makes it difficult for the antivirus software to locate them using signature or string searches (since they are very different in each encryption).

Polymorphic Viruses Include:

  • Marburg
  • Tuareg
  • Satan bug
  • elkern


Trojans can illegally trace important login details of users online. For example, E-Banking is very common among users, therefore, the vulnerability of tracing your login details whenever your PC is working without any strong, powerful antivirus installed.

12.Email Virus

This is a virus spread via an email. Such a virus will hide in an email and when the recipient opens the mail.

13.Browser Hijacker

This virus can spread in many different ways including a voluntary download. If infects certain browser functions especially in the form of re-directing the user automatically to certain sites. A good example is

Browser Hijackers Include:

  • the cool web search

14.Boot Infectors


They include the boot sector plus master boot record types. All the viral codes can be separate location; however they infect the hard disks or the floppy.

Boot Infectors Include:

  • The brain virus -it is the very first wild virus to be created.

From what we have seen, the many types of computer viruses and their effects are very harmful and can completely damage your system. Always make sure your system is up to date. Also, install antivirus software. The antivirus program protects your computer and the personal information in it.

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Some of the most common worms are email virus and Trojans. The viruses and worms are spread mainly in the following ways;

  • Files sent as email attachments
  • Via a link to a web or FTP resource
  • Via a link sent in an ICQ or IRC message
  • Via P2P (peer-to-peer) file sharing networks
  • Some worms are spread as network packets. These directly penetrate the computer memory, and the worm code is then activated.
  • Computer worms can exploit network configuration errors (for example, to copy themselves onto a fully accessible disk) or exploit loopholes in the operating system and application security. Many worms will use more than one method in order to spread copies via networks.

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Computer worms and viruses are known to exploit network configuration errors or other loopholes in the operation system and even the applications safety. You may be wondering what the virus does after it infects the system; the following is a clear explanation;

Some computer viruses are programmed to harm your computer by damaging programs, deleting files, or reformatting the hard drive. Others simply replicate themselves or flood a network with traffic, making it impossible to perform any internet activity. Even less harmful computer viruses can significantly disrupt your system’s performance, sapping computer memory and causing frequent computer crashes.

The computer virus may harm your computer, damage programs, reformat your drive, or delete files. Your computer may be infected if you recognize any of these malware symptoms:

  • Slow computer performance
  • Erratic computer behavior
  • Unexplained data loss
  • Frequent computer crashes

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The most ideal symptoms that you may have malware issues is the slow computer performance and unexplained data loss. Luckily, there is a vast range of solutions and preventive measures to protect your system, they include;

  • Use antivirus protection and a firewall
  • Get antispyware software
  • Always keep your antivirus protection and antispyware software up-to-date
  • Update your operating system regularly
  • Increase your browser security settings
  • Avoid questionable Web sites
  • Only download software from sites you trust. Carefully evaluate free software and file-sharing applications before downloading them.

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