Adware infections net the purveyors of slimeware software around $3 a year for each infected PC, according to estimates from anti-spyware firm Webroot Software. Using this figure and stats from its own malware auditing services, Webroot guesstimates the illicit advertising market underpinned by adware infection of home and business PCs could be worth up to $1.6bn a year. According to Richard Stiennon, VP of threat research at Webroot, the illicit ad market enjoys approximately the same growth rate as the legitimate market. But that's where the similarities end. "It [adware] has a similar bus model and some of the same...