I reported what I thought were invalid clicks to Google AdSense! I suddenly had a very high CTR ~10%! In my opinion, it was definitely artificial. So I told them and requested that my account be continued and any earnings accrued from such invalid clicks be deducted. I did not get any mail for almost a week and I was getting worried and was even expecting an account shutdown. Fortunately they replied and told that they have done an investigation and have found that some clicks were indeed 'invalid'. Though I cannot disclose here how much money was deducted, considering my usual monthly payment, it was substantial! Good thing to note is, since I reported them, my account is still alive!
It was not through the use of logs that I suspected, but just the "sixth sense". My usual CTR is in lower single digits. When it suddenly crosses double digits, in only one channel without any modification done recently, it arouses suspicion, doesn't it? That's what happened to me. Now I am planning to install adsense logger. Any suggestions?
If you suspected someone is doing that, why don't you remove your code for a couple of days until Google answers your email?
How did Googod decide what was and was not an invalid click? Did they tell you? Did they provide you IP addresses to block so it does not happen in the future?