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.

 (above wrıtıng www.microsoft.com from receipt)