This is a real issue – I am banned for Adsense after I explained the concept to a friend who promptly decided to be too helpful and click the ads many times. He even told a few friends to be helpful. All without me asking for it.

Really this is something Google should look at building direclty into Adsense. My site has grown significantly since I was banned, and so if there had been some way to prevent the click fraud other than banning me, they would now be getting more money!