A computer virus is a computer program capable of changing the way a computer operates and act without the permission or knowledge of the computer user. Computer viruses hide themselves inside other program files and are therefore easily transmitted. In everyday speech, the term computer virus is often used for a wide range of malicious programs, but the formal definition of computer viruses requires a program to be able to replicate and execute itself, otherwise it will not be a true computer virus.


There are currently many different types of computer viruses, included those listed below. * File viruses (parasitic/executable viruses)
* Boot sector viruses
* Multipartite viruses (boot sector virus + file virus)
* Macro viruses
* Network viruses
* E-mail viruses (any type of virus that kidnaps your address
   book and spreads itself to all your contacts)
* Companion viruses (including path companion viruses)
* Logic bombs and time bombs (can be parts of viruses or worms)
* Sentinels (can make it possible for its creator to remote control
   your computer)
* WB Microworms
* The invisible HaloViruses
* Cross-site scripting viruses (XSSV)

Many viruses are designed to cause damage, e.g. by deleting files, render programs unusable or even reformat the entire hard drive. Others are more of a prank, and will simply play an audio message, start a film, leave a text message or similar. The problem with these seemingly innocent tomfooleries is however that they occupy computer memory and can cause system crashes. A virus can also be filled with bugs and therefore cause the system to crash.


The first known computer virus that spread outside a single computer lab was “Elk Cloner”. Elk Clooner was created in 1982 by a 15 year old student named Rich Skrenta. The virus was put into a game and designed to release when the game was started for the 50th time. This computer virus worked with Apple DOS 3.3 operating system and spread via floppy discs. When a computer user would start the game for the 50th time, the screen would turn blank and a poem about the virus named Elk Cloner would be displayed.

There are several things that you can do to protect your computer from viruses and milder the effects of any computer virus that still manages to get in.

* Use a high-quality anti-virus program and keep it updated.
* Use a firewall.
* Use an updated operating system.
* Always be suspicious of programs and files sent to you over the
  Internet, including files that can be downloaded via Internet sites
  or P2P sharing programs.
* Make regular backups of important data, programs and your
  operating system. If a computer virus delete or alter the content
  of your computer, you can use the backups to milder the effects.