How does the cheat detector work?

Thibault (or whoever knows enough to answer my question), Recently the computer called a game (in my favor) and said "cheat detected." Presumably you have installed a cheat detector of some sort. How
does it work? Does it analyze for a "perfect" game, or look for games resembling a chess masters games? Or do certain chess engines prefer certain styles of play which your machine detects? Or does it
check to make sure that it isn't actually a chess engine connected to the server and not a real person? I cannot figure out how to do this without it being very fallible. I am interested in
programming, so details regarding how it works would be appreciated.

Thanks for such a wonderful site.

I forgot to include the replay and analyze link:

http://en.lichess.org/analyse/fmssbrpn/black

there are two distinct cheat detection systems operating. The one you encountered detects people who use lichess AI to cheat. That's what your opponent did.
The other one is more general but less precise. I don't want to let people know how it works, because it may reduce its efficienty.

But well, lichess is opensource, so if you really want to know what it does, go read the code :)

are you absolutely sure they're cheating? I was playing with a friend (I was Black, he was White) and the game suddenly ended:

Cheat detected
Black is victorious

Now, he was working at the time, so he was frequently switching windows. How can you be absolutely sure if they're cheating just because they're switching windows?

automatic cheat detected is when the algorithm detects 2 games with identical moves, one with AI, and one, reverse colors, with another player. The idea being, your opponent was playing your moves as
his own against AI, and playing AI's response as his own in your game.