You lost to a cheater

I've received this message. What is it or who, and why?

@Kate_16 You played a game. You lost. They cheated; it wasn't your fault. You'll possibly get some points back for it. Who - they don't say, but you can go back through your game history and hover over your opponent's name and it'll tell you.

Thanks.

Why is my student blocked? For a game that is a theory?

@Darmik "Cheat Detected" occurs when someone uses the Lichess Stockfish analysis board to cheat in the game. It can also happen if you play against Stockfish on Lichess with the same position.