This question was closed a few days ago: http://stackoverflow.com/questions/3578775/how-google-and-other-pay-per-click-companies-discover-click-fraud-closed
I'd welcome some discussion on whether questions such as that should be closed. In my mind it's a question regarding a software problem, which has a software solution - and therefore anyone interested in developing a software solution would be entitled to ask a question on SO.
If you think its not a valid question for SO, it might help if you specified where such a question would better belong.
Adding a bounty, because I think this hasn't got a conclusive answer yet. Most of the comments suggest its off-topic, but the question is now open and highly upvoted. Further if SO isnt the most relevant place, then lets have a conclusive answer on where these questions can go.