Don't know for sure, never had problems with clicks, not even from competitors or people who just wanted me out of business, not even the accidental click, or just because I was curious .. (you know, ads about your content, which you usually have an interest in, it's like christmas sometimes)
The thing is also, that google has alot of statistical information about almost every user, and can pinpoint most people, wether they are at home or in an internet cafe in paris. (personality profiles, demographics, user behavior, click-rates, interests, you know the fancy words, just look at your own statistics and think about what statistics google has..)
Anyways, I think it's very hard to mess around with adsense without getting either a warning or a ban. The latter is usually the case if it's serious enough, and it's pretty much always the webmasters own fault when it comes down to it. Google can be nice or not-so-nice, depends on your reactions and how you deal with things.
Just to make a case out of it : when I had a problem with some content I had added to an old website project which has long been abandoned, I didn't really thought the new content was in violation of the ToS, google apparently reviewed it for some reason, and then the google adsense team was nice enough to email me and point out some of the articles that were in violation of their tos and also mentioned that there were other articles which I should look at and address without being specific
Then I re-read the ToS very carefully, and then found the problems, addressed them appropiatly and sent them a reply a day later, that I had removed all content which I believed could in any way be in violation of their ToS after having re-read it and if they would be kind enough to review it to make sure I really had done everything I could.
The next day everything was fine and Adsense was showing again. Guess i'm lucky. Not many are that fortunate. Especially not people trying to game them and play smarter than they think they really are. Just my experience.
Sincerely and have fun,