It's becoming more and more necessary for computer users to take initiative in protecting their machines from viruses, worms, and other malicious software. These programs, spread via the Internet, take advantage of security holes in computer operating systems (OSes), Web browsers, and email clients, and wreak havoc with data.

Following the guidelines below will help you avoid problems caused by these invaders, and keep your computer healthy and your data safe.

Be careful when installing software.

When you download free or shareware applications from the Internet and install them on your computer, beware -- you may also be installing hidden programs that covertly gather information about you and your computing setup (spyware) or attempt to damage your system (malware). Many peer-to-peer file sharing programs used to swap files on the Internet, such as Kazaa, install such software. Windows users, who are most likely to have problems in this area, can download, install, and run the free version of LavaSoft's Ad-Aware application to clean up their systems

Don't click on popup windows.

While browsing the Web, you may encounter popup windows that try to entice you to click on them. Don't! By doing so, you may inadvertently allow the installation of harmful software on your computer.

One way to protect yourself from unsolicited popup windows is to install popup-blocking software. Some Web browsers include popup blockers; these include Mozilla and Mozilla Firefox (both available for Windows and the Mac OS) and Safari for Mac OS X.

Unfortunately, one potential drawback of installing this software is that it can block popup windows that you want to see and click on, as part of sites whose content is safe. (For example, iROCKET uses popup window functionality to present quizzes.) You may want to disable popup blocking software when accessing safe sites to make sure the sites work properly.

Keep your operating system updated.

It's also important to keep your computer's operating system up-to-date, to prevent malicious software from exploiting security holes in the OS. Some recent OS versions (e.g., Windows XP Service Pack 2, Mac OS X 10.3) can automatically update themselves, but users running older versions may need to perform manual updates -- Windows users can visit Microsoft's Windows Update Web site for this purpose.

Install anti-virus software, and keep it running and updated.

If you don't have anti-virus software installed on your computer, get some. There's a wide variety of anti-virus packages for Windows and Macintosh, and we recommend Norton AntiVirus for Windows and for Macintosh (both are available at The Source).

Don't open unknown email attachments.

Be careful with files that you receive via email, even if they appear to come from someone you know. Open only documents or images whose source and content you're sure about, and delete questionable attachments. When in doubt, contact the person who sent the file and ask her or him about it.