That's exactly what Microsoft alleges that three people did for insurance and World of Warcraft ads. The investigation went on for more than a year, and involved a game of cat and mouse where Microsoft would erect defenses against the manipulation, the alleged click-fraudsters would learn how to evade them, Microsoft would come up with new defenses and the process would repeat.
That's not a lot of money for a company like Microsoft, but the money isn't really the point here. Microsoft wants to set a legal precedent, sure, but the real point is to make click-fraud too expensive for the fraudsters.
"The theory is you can change the economics around crime or fraud by making it more expensive," Tim Cranton, associate general counsel for Microsoft, told the New York Times.
Microsoft Sues Three in Click-Fraud Scheme (NYTimes)
Microsoft files its first click fraud lawsuit (Seattle Times)