I signed up for a Google AdSense account a few weeks ago and was testing it on several web sites (this is the program that pays you when users click links fed to your site by Google AdWords). Last week they sent me an e-mail saying my account had been closed due to illegal clicks. Since their tracking methods are a closely guarded secret, they wouldn't say what was wrong or how they made their determination. I used their appeal process and asked them to reconsider. They re-opened my account and I did notice that one of my end users had a couple of days with an extraordinarily high percentage of click-throughs. I think that he may have been using the displayed ads to check out the competition not realizing that this was costing the advertisers money and putting his participation in the program in jeopardy. I contacted my client and explained the rules so this won't happen again. So far the return on this program for my clients is averaging pennies a day but I'm going to keep it running for a while. I am using their search tool on one of my client's sites and that works quite well.