But honestly, I think you went into a bit of bad luck. We do not get such cheaters very often. Most of the time cheating someone is just another word for deceiving/lying on the diplomatic part of the game (Copyright Kutuzov, PBW Paranoia TM

). I'll try to be very careful on replacement players, but should your cheater have been a bit more careful, he would have stormed the game without any possibility for you to understand what was going on.
Last, I prefer a max of 10 players. You have less dropout then.
PS : Atrocities, you are NOT a newbie.
