They are little pieces of Web code used mostly to track people's online behavior. Bugs can, however, be written to reach across the Internet into unprotected computers and steal files. By masking the numerical Internet address that identifies a user's computer, Web sites are prevented from tracking the user, who effectively surfs under an alias. Dozens of other privacy protection products exist, including Privada, Anonymizer, IDzap and Somebody. About a half dozen privacy products block banner ads and some are effective against Web bugs, says Richard Smith, chief technologist of the Denver-based Privacy Foundation.
Web bugs can be fairly innocuous, providing advertisers with data on who is visiting a Web site.
Or they can be intrusive, passing information that surfers enter into online registration forms to advertisers or marketers, said Smith. Web bugs need cookies to function. Tommy Wang, director of the Pittsburgh security startup Intelytics, says about 85 percent will set a cookie on an unprotected surfer's computer. So it's sort of putting social pressure on Web sites. Intelytics is working on a product called Personal Sentinel that Wang said would work similarly.