A computer virus is a program that invades your computer system, hides there, and makes copies of (replicates) itself. Viruses spread when you launch an infected application or start up your computer from a disk that has infected system files.

Viruses behave in different ways. Some viruses stay active in memory until you turn off your computer. Other viruses stay active only as long as the infected applications is running. Turning off your computer or exiting the application removes the virus from memory, but does not remove the virus from the infected file or disk.

Some viruses are programmed specifically to damage the data on your computer by corrupting programs, deleting files, or erasing your entire hard disk.

All computer viruses are manmade. A simple virus that can make a copy of itself over and over again is relatively easy to produce. Even such a simple virus is dangerous because it will quickly use all available memory and bring the system to a halt.

Trojan horses are not viruses; however, they are often thought of as viruses. A trojan horse is a program that appears to serve some useful purpose or provide entertainment, which encourages you to run it. But, like the Trojan horse of old, it also serves a covert purpose which may be to damage files or perhaps plant a virus on your computer.

Many computer viruses turn out to be hoaxes or myths. Hoaxes are false alerts about viruses that don’t exist. For a list of hoaxes check out Computer Virus Myths and Snopes.

We highly recommend that you have Virus Protection installed in your computer before you consider downloading anything. Here are the most popular anti-virus websites:

Symantec
Provides content and network security software and appliance products to individuals, enterprises, and service providers.

McAfee.com
Provider of software application services for PC users.

Network Associates
Supplier of enterprise-wide network security and management software.