Computer viruses are software programs deliberately designed to interfere with computer operation, record, corrupt, or delete data, or spread themselves to other computers and throughout the Internet, often slowing things down and causing other problems in the process.

Just as human viruses range in severity from the 24-hour flu to the Ebola virus, computer viruses range from the mildly annoying to the downright destructive, and come in new and different forms. The good news is that with an ounce of prevention and a little knowledge, you are less likely to fall victim to viruses and you can diminish their impact.

How do viruses work?

Basic viruses typically require unwary computer users to inadvertently share or send them. Some viruses that are more sophisticated, such as worms, can replicate and send themselves automatically to other computers by controlling other software programs, such as an e-mail sharing application. Certain viruses, called Trojans (named after the fabled Trojan horse), can falsely appear as a beneficial program to coax users into downloading them. Some Trojans can even provide expected results while quietly damaging your system or other networked computers at the same time.

Although it's good to be aware of these different types of viruses and how they work, what is most important is that you keep your computer current with the latest updates and antivirus tools, stay current about recent threats, and that you follow a few basic rules when surfing the Internet, downloading files, and opening attachments. Once a virus is on your computer, its type or the method it used to get there is not as critical as removing it and preventing further infection.

To learn more about viruses, read other topics in this series including How do I know if a virus has infected my computer?, How do I remove a virus?, and How do I protect my computer against viruses?

This article is provided by the Microsoft Security at Home website. For more information, please visit http://www.microsoft.com/athome/security/viruses/intro_viruses_what.mspx