Computer Virus


Computer viruses are programs within the computer or from the internet which can cause harm to the computer itself or to the computer network. 'Virus' is a commonly used term in computing which includes many different types of computer threats e.g. malware, worm, Trojan horse, logic bomb and so on. A virus can be injected in a computer in many ways for example email viruses, trojan horses, worms etc. Microsoft suggested a clear and precise definition for computer virus. They said:

“A computer virus is a small software program that spreads from one computer to another computer and that interferes with computer operation. A computer virus may corrupt or delete data on a computer, use an e-mail program to spread the virus to other computers, or even delete everything on the hard disk.” [1]


Computer viruses are most simply spread by attachments in email messages or by instant messaging. So you must never open an e-email attachment unless you know the person sent the message, or unless you are expecting the e-email attachment or from a trusted source; in which case, read the sending email address correctly and re-evaluate if the email address is of a trusted source.
Computer viruses can spread by using downloads on the Internet. They can also be concealed in pirated software or in other files. Computer viruses also can damage the data on your computer by corrupting programs.

The software that has a malicious purpose is harmful for your computer and we consider them as virus, worm, Trojan horse, logic bomb, Rootkit etc. Some of the computer virus contains self-replicating code attached to some other piece of code, some of them are self-contained program which propagates independently, some of the viruses are with hidden effects which are not intended by the user executing the program, some of them get only executed if a specific trigger condition is met and some of the viruses can modify or replaced your operating system files to conceal unauthorised activities. All activities by the computer viruses can cause collateral and internal damage in your computer. The symptoms of computer virus can infect your computer in many different ways.

Symptoms of Computer Viruses

The following symptoms may be seen if a computer is infected by virus:

  • Computer becomes slow and it takes more time to start than it is supposed to take.
  • Anti-virus software will alert you about the computer virus.
  • Your Operating system will take a long time to start, in some cases OS does not start even though you didn’t make any system changes.
  • You will receive some error messages; for example, ‘New programs are installed incorrectly’.
  • The partition of your computer’s hard disk will have disappeared.
  • Your computer will frequently stop responding and will often lock automatically.
  • Applications in your computer will not work as anticipated.
  • A very strong virus can disable your anti-virus software and also you will be unable to restart the anti-virus.
  • Virus can damage the disk/cd/dvd or disk drive so the disk/cd/dvd or disk drive will be inaccessible.

There are many more symptoms which depend on the type of viruses. Therefore, if you see any of these symptoms in your computer more likely your computer is infected with virus.


We all know that the prevention is better than cure but it is difficult to prevent the computer from viruses because we all use unknown software and we visit many web pages which may contain virus. However, if we take precautionary steps such as set up anti-virus software and always use the updated version of it, do not use any unauthorised software, before using any USB flash drives always scan them; visit only legitimate websites and so on, these guidlines may prevent your computer from being infected by a virus or viruses. In some occasions anti-virus is unable to detect and delete the virus, in that case we need to try other anti-virus software because sometimes a specific anti-virus is useful for a specific virus.


1. Microsoft Corporation (2012), Computer viruses: description, prevention, and recovery [Online], Microsoft Help and Support. Available from: (Accessed date 07/03/2012)

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