A Layman's Glossary of Malware Terms

The Trojan horse perpetuates click fraud, a scam in which Web advertisements are clicked in excess or under misleading circumstances in order to generate revenue for those who own the Web pages the ads appear on.

The malware, called "FFSearcher," is "one of the more clever" ones seen of late, wrote Joe Stewart, director of malware analysis at SecureWorks, on a company blog.

The Trojan that SecureWorks analyzed revolves around the use of a widget made available to webmasters from Google. Google offers a custom search box that can be embedded in Web sites, which enables access to its search engine and also shows AdSense advertisements.

If someone clicks on an AdSense ad, Google will pay the Web site operator "a small sum of money," Stewart wrote.

For PCs that have been infected with FFSearcher, all searches the person does on Google are invisibly channeled through another Web site called My Web Way, which uses Google's search widget. The user sees search results that appear to come from Google but actually are first channeled through My Web Way. Even the URL box indicates the results come through Google's domain, Stewart wrote.

What the creators of FFSearcher are hoping is that those infected users will also click on AdSense ads, which My Web Way will get credit for. Google loses since it pays those fees. My Web Way appeared to be no longer active as of Wednesday afternoon.

A Google spokesman said the company has taken steps to disable the AdSense for search accounts affiliated with the Trojan. Advertisers were not directly hurt, the spokesman said.

FFSearcher works with the Firefox and Internet Explorer browsers. An analysis of the code showed that Yahoo also appeared to be a target, Stewart wrote.

The problem with FFSearcher is that it may be difficult for search engine companies to detect the fraud since the behavior of users is no different than normal, Stewart wrote. Google and other companies use technology that can, for example, detect when an automated program or bot is repeatedly clicking on an ad in a behavior inconsistent with the way a human would interact.

"FFSearcher undoubtedly raises the bar for the fraud detection teams working at the major search engines," Stewart wrote. "It will be interesting to see how they combat it and other trojans using the same technique in the future."