I've used the ultimate trainer on multiple accounts to complete the campaign, all challenges, and the vs. A.I. achievements, but is there more of a danger playing against A.I. from multiplayer vesus single player? I really want to know because I want the achievements for custom games, but don't want to risk my main account. I think the real issue is when the trainer is running and any offsets are changed then they play a co-operative or quick match game, but I don't do that at all. Can anyone confirm it is still safe to do this?