I suspect I was a victim of a version of this fraud years ago. Lots of suspicious clicks off of strange queries or weird AdSense blogs (the latter might have been the more straightforward AdSense fraud) and the visitors rarely engaged with more than one page.

Google insisted that if there are any fraudulent clicks, they are detected automatically and we are not be charged for them. But it was essentially impossible to know if that's true. I guess it doesn't really matter: at the end of the day you tally up your metrics and AdWords is either worth it or not. Still a very frustrating experience.