my frnd got this mail from google... While going through our records recently, we found that your AdSense account has posed a significant risk to our AdWords advertisers. Since keeping your account in our publisher network may financially damage our advertisers in the future, we've decided to disable your account. Please understand that we consider this a necessary step to protect the interests of both our advertisers and our other AdSense publishers. We realize the inconvenience this may cause you, and we thank you in advance for your understanding and cooperation. If you have any questions about your account or the actions we've taken, please do not reply to this email. You can find more information by visiting https://www.google.com/adsense/support/bin/answer.py?answer=57153&hl=.... Sincerely, The Google AdSense Team and he did not do any illegal with this... why his acc banned.... he got his first chq now .... his acc is not banned for invalid click... can he cashed it in a bank???
If your friend really thinks the decision is wrong, send a detailed (with stats) and polite reply to Google.