Whenever I spotted a hacker, I would just delete them from my friend list, and move on, but I've had it...
The ones that frustrate me is the ones continously trying to add me. I forget they hack and I add to do a repeat delete. This happens quite often with me.
I used to have a note on my iPhone with all the names of the hackers I've spotted. Stopped tracking... I've also started to report them to Apple, with the claims they hacked the IAP system. Don't know if that'll do any good, but I'd like to think so.
I've played this for 3 days total time, and then finally understood that I will never get all cars. Even after having spent quite a lot on IAPs. So I went ahead and added all cars. I gave the game all I could, and now it's time to get all it can give. Don't see anything wrong with that. You can't hack driving skills, you know...