I was playing a game on Lichess the other day and all the sudden the system ended the game, awarded me the victory, and said "Cheating by White detected". How in the world could you cheat on the Lichess site ? Does anyone know what this means? My rating is 1250 ...... who would bother to cheat against me ?

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    VTC because this question is completely primary opinion based. Anti-cheat policy can be found on Lichess site, and only Lichess staff can answer you why you're identified as a cheater for your particular case.
    – user17931
    Nov 26 '19 at 2:02
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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 '19 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 '19 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 '19 at 21:36
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    @lbragile ...Proof are everywhere? If you go look at r/chess subreddit, there are lots of posts that object to lichess cheating claims, and lichess mods often do respond to these posts.
    – user17931
    Nov 27 '19 at 2:33

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?


  • 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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    @TomášZato Possibly by timing the moves. The difficulty would be telling the difference between players who had memorized opening moves, and those who were using opening books. Possibly detecting a pause where the player turns to a different page to handle a particular variation. Nov 26 '19 at 11:15
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    You can not reliably detect book cheating. Variation in timing might also be just by getting up to the toilet, getting a cup of tea or whatever. Nov 26 '19 at 13:13
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    @infinitezero Not limited to chess: You cannot reliably detect online cheating, period. Never play for money; prefer to play with people who you know. Nov 26 '19 at 13:43
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    It's mostly probability testing they use, IIUC. If your moves happen to match 100% what Stockfish would do, that's impossibly unrealistic. Even GMs don't hit that accuracy, since human play is different from engine play even in the higher ELOs. A GM/FM/IM/etc may score above 80% or so, but it will differ from an engine and a trained system can detect the difference.
    – Mast
    Nov 26 '19 at 13:57
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    @Mast that's right, chess.com shows this in their analysis features, they have by far the most advanced features that I can find online. See my answer below for more details :)
    – lbragile
    Nov 26 '19 at 21:33

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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