Mark, the guys at Google didn't tell me exactly how they were able to determine the clicks were fraudulent, but it was pretty obvious what was going on. Just the fact that the ctr jumped from 1.5-3% ctr to 35-40% ctr alone is enough proof in my mind. Either way, they said they would take measures to prevent this in the future.
I can share what I know about hitbots, however. I'm not an expert, but I've had past experiences with cheaters and hitbots on sites and toplists I've run in the past, as well as some experiences with other ppc engines. Essentially, the way a hitbot works is to create artificial clicks through the use of hundreds of proxy servers. As a result, Google's tracking software sees each click as a unique surfer clicking the ad and counts each click. This is different from a competitor physically clicking on your ad over and over, since they will be doing this through one IP address, so Google will only count one of the clicks since all are coming from the same user.
Finding evidence of a hitbot is difficult, since in some cases sophisticated software is used. What you have to look for in your server logs is proxy server IP addresses, and a lot of activity from proxy server IPs. Sometimes, the person's IP can show through as a few of the proxy servers may not be anonymous. This is how you can catch the person who is attacking you. But like I said, this is difficult to do. And the other problem is that a lot of legitimate traffic comes through proxy servers as well, so this makes things even more complicated.
The only advice I can really give is to watch your campaigns and know your traffic. All traffic establishes trends over a period of time. If you see any prolonged suspicious, or drastic changes in traffic patterns, then you may have a problem. If you are convinced that you do have a problem, do not waste a lot of time with the front line client services reps. I did not find them very knowledgeable or helpful, and it was only when I moved up the chain of command that I found people who knew what I was talking about and were able to produce results.
Cheers!
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