I can see both sides. I do disagree with Google unable to share the reports of the activity in order to protect their detection. Google can feel free to protect their detection, but they should at least give you a reason as to why they came to that conclusion, because without it, any mistake that may have occured would/will not be found. This doesn't just go to you, but to the hundreds of others who post here each month with "being banned".
What a conclusion that we can make is that THEY RULES. They can do anything, deduct your money etc. It's their money anyway. Play safe...
i think this kind of letter is better rather than being ban from adsense. but i think they should give us a report what clicks in our adsense is invalid.