What is a computer virus?

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 to slow things down and cause 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.

Note: No known viruses have the ability to damage computer hardware such as disk drives or monitors. Warnings about viruses that can cause physical harm are either hoaxes or misinformation.

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 you surf the Internet, download files, and open attachments. Once a virus is on your computer, its type or the method it used to get there is not as critical as it is to remove it and prevent 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?

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