The SiteAdvisor software, which works with both the Internet Explorer and Firefox browsers, draws on information compiled from millions of automated Web site visits to let users know whether visiting these sites is likely to yield annoyances such as spam, spyware or computer viruses.
SiteAdvisor warns users when they are visiting untrustworthy Web sites by placing a red "X" in the bottom corner of the browser. A yellow exclamation mark means that users should be cautious because tests have revealed some issues with the site, and a green checkmark means that the site is trustworthy.
With the Google, MSN, and Yahoo search pages, SiteAdvisor actually superimposes its ratings icons right on top of items in the search results, making it easy for users to see when they may be on the verge of clicking on a dubious Web site.
SiteAdvisor believes that unwitting Web surfers make more than 1 billion visits to untrustworthy "red" sites every month.