Viruses are nasty little pieces of computer programming code that make your computer do things you didn’t want and didn’t authorize. The category of unwanted critters is called malware, or malicious software. Malware comes in different varieties, including true viruses and programs called Trojan horses.
True viruses are self-replicating: They attach themselves to a file, and every time the file is opened, the virus is opened and activated. Viruses also can reside in computer memory, and each time your computer opens or modifies a program, it activates the virus. Over time, left unchecked, the virus will replicate itself onto many programs.
A Trojan horse technically isn’t a virus because it doesn’t replicate itself and spread to other programs. Instead, it’s a program that appears to be one thing, but is actually something else. For example, you could download a program that you believe to be a new game. Once launched, however, the program is really a “stealer” a program designed to steal your user name and passwords.
Guarding against viruses, Trojan horses and other malware is as easy as buying and installing anti-virus software. The most popular manufacturers are McAfee (VirusScan) and Symantec (Norton Antivirus software). With more than 500 viruses discovered weekly, these companies keep close tabs on the latest malware.
When you buy and install an anti-virus program, you can configure it to automatically scan your incoming and outgoing mail, e-mail attachments and downloads. This ensures that you can open an e-mail attachment without worrying that it’s carrying a known virus that will infect your system. (Note: The text portion of e-mail messages cannot contain a virus. The only way to get a virus from an e-mail is to open an infected attachment. The virus rides along in the attachment, not the e-mail message itself. Be cautious about opening attachments, even when they appear to come from someone you know. Viruses and other malware called worms can “borrow” a recognizable e-mail address, so the attachment may look like it comes from someone you trust.)