Viruses
Just like a virus that passes from person to person, a computer virus passes from computer to computer. Viruses attach themselves to a program or file on a computer, then "infect" other programs and files. The best preventative measure is to install reliable virus detection software.
How do I protect my computer against viruses?
You must continually update your computer's operating system and your virus detection software. For example, Microsoft regularly prompts consumers to download updates. The updates protect your computer against new virus outbreaks.
TIP: Do not open e-mail attachments with the file extensions: .EXE, .COM, or .VBS. Those attachments are really programs that may damage your computer.
What is a "worm?"
A worm is a special program that copies itself over and over as it jumps from machine to machine. Worms infect other computers through networks linking many different computers.
What is a Trojan horse?
A Trojan horse is a computer program that appears to be one thing (a game, for instance) but instead is programmed to damage your computer. For example, it may erase your entire hard drive. Trojan horses often lurk in e-mail attachments.