12. What is a computer virus?

A computer virus is sophisticated software that can install itself and run on a computer without the permission or knowledge of the user. Once running, it will try to set up copies of itself on any other computer the infected machine is in contact with (hence the term 'virus'). All this is done usually with criminal intent, either to cause damage to data and software, or to steal information either from or via the infected computer.

Computer viruses are part of a group of increasingly sophisticated computer programs, collectively called “Malware”, which is short for "'malicious software".

This group also includes computer Worms and Trojan Horses as well as Spyware, often designed to work in tandem with each other in order to conceal their individual presence. An extreme form is the "rootkit", which is carefully designed to leave little or no sign of its operation, even to computer specialists.

Infected computers with internet connections can be controlled remotely by the perpetrators. The machines become part of 'botnets' (robot networks)—groups of compromised machines remotely controlled, that are used by their new 'owners' to mount hacking attacks, send out spam email messages, or perform other cyber-crime tasks.

The internet is estimated to have millions of infected machines connected to it, and thousands of botnets operating, stealing passwords, attacking web sites, government and business networks.

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