Compare that with the Trojan Horse strategies of rivals Claria (once known as Gator) and WhenU: Their software is often embedded in games or screen savers that many people download unknowingly. (The companies insist they give fair warning of what you're downloading in their click-on licenses.) "No need to be obnoxious, " says Keith Smith, 33, who founded 180 in 1999.

FORBES: Mr. Manners

And even though Microsoft has a feature in its Internet Explorer browser designed to steer users away from unknown and potentially untrustworthy software, about 5 percent of users ignore the warnings and download malicious Trojan horse programs anyway. via Microsoft: One in 14 downloads is malicious.

FORBES: Users on Self-Destruct! Make 'em Pay!