Though these terms are often used interchangeably, they refer to different types of malicious computer programs.
Computer viruses hide within other programs or documents and spread as a side-effect of user action (e.g., opening an attachment). They come in many forms, and you don't need to install a program for your computer to be infected. For example, some viruses are spread when you open a word-processing document, particularly if you have macros enabled. Once your computer is infected, the virus may attach itself to outgoing files or may be sent as an email attachment.
A Trojan horse is a program that disguises itself as another program. Similar to viruses, these programs are hidden and usually cause an unwanted effect, such as installing a back door in your system that can be used by hackers. They differ from viruses because they typically are not designed to replicate like a virus.
Worms spread without any user interaction, typically by exploiting a flaw in popular software. Once activated, they generally use the Internet or your LAN (local network) to self-propagate and often take advantage of vulnerabilities in Microsoft Outlook and Microsoft Outlook Express email programs.
Protecting Yourself and Your Computer
Here are some ways to protect yourself and your computer against these programs:
Use anti-virus software. To learn more, please search for Virus Protection in Yahoo! Search.
Download anti-virus software updates frequently. They are usually posted weekly, and generally only take a couple of minutes to download.
Scan email attachments and programs downloaded from the Internet. Yahoo! Mail lets you use Norton anti-virus software to scan your attachments before downloading them to your computer (learn more). If you receive attachments you aren't expecting or from someone you don't know, do not open the attachment. Even if you know the sender, you should scan the attachment in all cases.
Turn off the feature in email programs that automatically open attachments.
Don't install unfamiliar programs. Unless you know exactly what a program does and how it will affect your computer, don't install it.
Carefully read pop-up warnings. Many unscrupulous companies use pop-up advertising that falsely appear to be warnings. The pop-ups (which appear on sites other than Yahoo!) encourage users to install corrective software. These pop-ups should be ignored.
Verify email warnings. You may receive an email warning that claims to be from a computer "expert" warning you of a virus. Such emails usually instruct you to take certain steps to protect your computer. These are usually a hoax -- before following the steps outlined in any email, research it online by searching for Computer Virus Hoax in Yahoo! Search.
To learn more, please visit the Viruses and Worms category in the Yahoo! Directory.
