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Not long ago, Web- and e-mail-borne viruses were a computer user's worst enemy. Though viruses and worms still cause more damage in compromised or lost data, a newer menace, popularly known as spyware, steals users' productivity and peace of mind. The "spyware" label can apply to legitimate but annoying programs that users consent (perhaps unwittingly) to have installed on their PCs, or it can describe programs that install themselves without permission. Both types of applications can drain your computer's resources, slow your Internet connection, spy on your surfing, and even forcibly redirect your Web browser. For the purposes of this story, we'll call the former category adware and the latter spyware. Adware clearly spells out its intent, comes with an uninstaller, and can be readily removed from a system. Spyware, in contrast, installs itself surreptitiously and can be nearly impossible to remove without assistance.

A crop of anti-spyware programs has sprung up to provide that assistance. We evaluated ten current anti-spyware utilities designed to detect and remove spyware and adware from PCs, looking at their rates of detection, scanning speed, ability to prevent unwanted applications from installing themselves, and ease of use. We were pleased to find that a couple of the programs did a very effective job of cleaning an infected system and preventing new infestations with effective real-time protection.

PC World tested seven products in the $20 to $40 range from big and small vendors: Allume Systems' (formerly Aladdin Systems') Internet Cleanup, Aluria Software's Spyware Eliminator, Computer Associates' ETrust PestPatrol Anti-Spyware, InterMute's SpySubtract Pro, McAfee's AntiSpyware, Sunbelt Software's CounterSpy, and Webroot Software's Spy Sweeper. In addition, we tested two popular free programs--Lavasoft's Ad-Aware SE Personal and Safer Networking's Spybot Search & Destroy--and a third free program that operates very differently but no less effectively, Merijn.org's HijackThis. (You can get all three free products here.) We did not include HijackThis in our charts because, unlike the others, it does not scan for infections. We also tested one product in beta, Microsoft's new Windows AntiSpyware, which was until late last year Giant Software's AntiSpyware. (See "Future Windows AntiSpyware Looks Like a Winner.")

We pitted the anti-spyware utilities against 45 adware and spyware programs we've frequently run into in our work. These 45 applications created 81 separate files and processes--which proved a challenge for our apps to remove completely. Spyware infections can begin with a single installation of advertising-supported software. Often, the adware alerts the user to its intentions and the user willingly makes the trade-off in exchange for access to the free program (or blithely clicks the agreement without reading it). But although many adware programs seek your approval prior to installation, not all are so obliging. And even the free application that promises only limited advertising can morph into a system full of spyware by downloading and installing third-party applications.

Adware varies considerably in how it gets on your system. Two common search toolbars we encountered, Slotchbar and WinTools, did not show an End User License Agreement (EULA), in which adware typically declares that it may install additional components. These two installed without our consent and proved the most difficult to remove, using multiple processes that reinitiated one another when anything tried to delete them.

In contrast, the common adware applications WhenUSearch (a search toolbar) and Bonzi Buddy (a desktop companion that offers search assistance) presented easily understandable EULAs prior to installing and provided an effective uninstaller through Windows' Add or Remove Programs utility.

• CounterSpy and Spy Sweeper Lead the Field (chart)
• Cleanup
• Cleaning Up the Mess (chart)
• Another Road to Success
• Real-Time Monitoring
• Beta Update: Future Windows AntiSpyware Looks Like a Winner
• Protect Yourself Against Spyware: Change or Update Your Browser
• Glossary