As a follow up to my entry just a minute ago named AdSense Click Fraud Revenge there is an other WebmasterWorld thread related to this topic. The thread is named Contacting Google After Suspicious Activity where a member asks, what is the benefit of contacting Google about this?
One senior member says "but if Google see fraud they'll kick you out without explanation or conversation. At that point it's unlikely that you can get their decision overturned. Not impossible, but very unlikely." But another member wrote, "I have emailed G before when I have noticed strange things happening and they normally have got back to me within 24 hours saying "nothing to worry about."