IBM's virus warning site 4. Computer Virus Myths 5. Symantec's Anti-Virus Research Centre 6. Basically, a computer virus is a program that is able to make copies of itself. These programs are usually designed with malicious intent.
Computer viruses travel by attaching itself to other programs and reproducing.
Some viruses are harmless and just create a nuisance, but others are intended to alter data or destroy an entire hard drive. The virus protection programs have to come with updates because new viruses are being discovered everyday. The virus lives in the host program and each time the host program is executed, so is the virus. At each execution, the virus seeks out more hosts to attach to. It spreads to numerous systems by attaching itself to as many hosts as it can and then making copies of itself.