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I was playing a game on Lichess the other day and all of a sudden the system ended the game, awarded me the victory, and said "Cheating by White detected".

How in the world could you cheat on Lichess? Does anyone know what this means? My rating is 1250 – who would bother to cheat against me?

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    That message usually only occurs if someone actually has the audacity to use lichess' own analysis board to get the best moves for your game WHILE playing you. As for the motivation: People really like imaginary internet-points (like your lichess rating...) - some will do unethical things to raise them, e.g. cheat in online chess. Nov 26, 2019 at 7:19
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    I've also (unknowingly and unintentionally) been flagged in a game as a cheater for having the Lichess analysis open at the same time as playing (and analyzing my moves as I played them). Nov 26, 2019 at 17:41
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    @TheHonestAtheist, analyzing your game while you are playing is technically cheating as you are getting information about your position which gives you unfair advantage in terms of extra outside information.
    – lbragile
    Nov 26, 2019 at 21:36
  • Several issues with this question: (1), this question is very oppinion-based, and it is not focussed on one question. It first asked for "What the Msg mean" and it goes on to ask for "Why would this player cheat against a 1250 player". Clearly, this question should be closed.
    – user26887
    Jan 7 at 21:12

2 Answers 2

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How could you cheat? This is what the Lichess terms of service say about it:

Cheating. We define this as using any external assistance to strengthen your knowledge and, or, calculation ability to gain an unfair advantage over your opponent. Some examples would include computer engine assistance, opening books (except for correspondence games), endgame tablebases, and asking another player for help, although these aren’t the only things we would consider cheating.

The most common form of cheating is using an engine. I don't know the details of what Lichess does, but cheating detection can consist of comparing a player's moves to those proposed by various engines, and based on statistical analysis one can come up with criteria for when the player's moves were "suspiciously similar" to an engine's.

Lichess also allows people to register bot accounts, but those must be clearly labelled as bots. So I suppose that another form of cheating could be to create a bot account and pretend that it is a human.

I also found this old FAQ:

  1. How are cheaters identified?

A:

  • Using the suspicious games themselves. The degree to which computer players differ in playing style and strength, to most human opponents that rely on them, is in most cases enough to reverse-engineer information from the game beyond what moves were made.
  • Using the player's other games. A player's profile shows all their games, including games where it is apparent that there was no cheating. Games where a player cheated and games where a player did not cheat have very different results when reviewing them using a chess engine (or Lichess' computer analysis feature).
  • Using the player's history. On every player's profile are public graphs of rating and average history, game database exports upon request, and win to loss ratio.
  • Time statistics. Anyone can see the public time consummation information for games, i.e., the time-per-moves.
  • A statistical analysis of the suspected user's playing behaviour. This statistical analysis is only visible to the lichess team.
  • Copying and pasting the suspicious game(s) into an engine and seeing how similar the moves are.
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  • Lichess monitors your mouse movements and can detect switching back and forth between browser and engine. Check the javascript. Note that this is by no means foolproof, but it catches a lot of people anyway.
    – Joshua
    Feb 19, 2021 at 16:32
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If you go on chess.com you will see that you can analyze games in a lot of detail. This analysis can compare to state of the art chess engines and determine whether your moves were "human-like" in their accuracy (for each piece) or if you simply made "engine-like" moves. For example, if each one of your moves was classified as the best possible move in that position - that would raise a flag especially if your rating is nowhere near the engine that would struggle to make those moves.

On that note, if you play on lichess (slow games), your opponent could theoretically use the board editor and analysis tools to make your moves and see what the computer would do in response. Then they would simply play those moves against you.

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