Is your PC feeling sluggish? Has your browser recently acquired a mysterious new toolbar? Are new programs showing up unexpectedly in your system tray? Do advertising windows pop up even when you're not browsing the Web? Have you discovered surprise 900-number charges on your phone bill?

All of these are telltale signs that your computer is beset with adware, spyware, or other malicious software you don't want and don't need. Like viruses, these programs often sneak onto your PC by piggybacking on a downloaded program, e-mail message, or Web site. Though not as dangerous as viruses, adware, spyware, and other unsolicited software can slow your PC, bog down your Internet connection, reduce your productivity, and jeopardize your personal privacy.

You can avoid installing unwanted software by being choosy about the free programs you download, and by understanding your browser's security settings. Removing adware and spyware can be tricky, but several free utilities detect and remove hundreds of known nasties.

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