A computer virus is a piece of unauthorized software added to a computer which automatically spreads itself to other computers. Some viruses do malicious things, such as erasing files or copying sensitive information (like passwords and credit card numbers).
Process of transmission
There are three main ways a virus is transmitted.
- Automatic replication. When you run an infected program, the virus also runs, searching your computer for other programs to infect.
- By email. When email software is configured to run programs attached to messages, the virus asks your email software to send it to recipients in your address book.
- Misleading advertising. A "Trojan Horse" is a program which seems useful, but contains a virus. The main program may or not perform as advertised, but the distributor knows it is infected.
A virus which infects networks is called a "worm".
A Trojan Horse virus typically does not replicate itself but is spread when you copy the program.
Configuring your email software so that it never runs attached programs is an easy way to stop email viruses. This should be the default setting, especially for corporate systems.
Virus scanning software is available from Norton, Symantec and other companies. The software detects the virus and removes it from infected programs.
It is also prudent to avoid trying out free games and animations available on the Internet. Reputable software companies go to great lengths to ensure virus-free software, so stick to these. Or else, use a separate computer for trials.
Discussion of the virus problem is sometimes hampered by the terminology used by purists, who distinguish between such varieties as "worm", "Trojan Horse", etc. But the generic term for unwanted software that infects your computer is "virus".