The rules of the US Chess Federation (USCF) prohibit using chess engines to help analyze a correspondence chess game that is still in progress. My opponent used Stockfish 6 to help him decide whether or not to trade rooks and to accept my draw offer. I did not discover this illegal use of a chess engine until after the game was over and I started to look at it with my own engines. I did not file a complaint about this because the use of this engine did not affect the outcome of the game. I got the draw that I wanted.
It is impossible to go into the engine room at playchess.com without using your own engine. Checking to see if someone else has analyzed a given position in the engine room could be considered cheating by a strict interpretation of the rules, but I will allow it because I do that too. What I object to is someone staying there more than a minute. If they are there long enough to get credit for discovering a position, then they are definitely cheating!
Posted below are screenshots of the engine use.
