A few years ago, the chess website Chess.com temporarily banned US grandmaster Hans Niemann for playing chess moves online that the site suspected had been suggested to him by a computer program. It had reportedly previously banned his mentor, Maxim Dlugy.

And at the Sinquefield Cup earlier this month, world champion Magnus Carlsen resigned without comment after playing a poor game against 19-year-old Niemann. He has since said this was because he believes Niemann has continued to cheat recently.

Another participant, the Russian Grandmaster Ian Nepomniachtchi, called Niemann’s performance “more than impressive”. While Nieman has admitted to sometimes having cheated in previous online games, he has strongly denied ever cheating at a live chess tournament.

But how does Chess.com, the world’s biggest chess website, decide that a player has probably cheated? It can’t show the world the code it uses, or else would-be cheaters would know exactly how to avoid detection. The website states:

Though legal and practical considerations prevent Chess.com from revealing the full set of data, metrics and tracking used to evaluate games in our fair-play tool, we can say that at the core of Chess.com’s system is a statistical model that evaluates the probability of a human player matching an engine’s top choices, and surpassing the confirmed clean play of some of the greatest chess players in history.

Luckily, research can shed light on which approach the website may be using.