Click fraud is not a concern with me as an investor for various reasons. First of all, companies like overture, i believe(cant find the article right now), have software that use filtering algorithms to weed out this problem. I am sure that goog and the rest are just as up on the technology as them. Secondly, Fraud is fraud. On the net it would be interstate thus federal crime, no?,(please correct me if i'm wrong here) but it seems rather stupid to risk something like this. Any ways after reading about the proprietary algorithms(secret) I'm sure they work fine. After all, a persons IP address is logged as well as other info. They can find you if they want.