World of Warcraft tracks exactly how long you have spent in the game playing it, you can type in /played to find out how long you have played for.
Ive seen screenshot evidence of some people who have spent over 365 days in the game.
That's an insane amount of time to spend in a game imo, but i guess if people who play this much have nothing better to do, why stop them? their clearly content to spend that much time in the game and not harming anyone else.
People in China have died playing the game, basically they stay up overnight and don't eat or drink because they are so absorbed by the game, they end up passing out because of exhaustion and don't recover, one woman has died and two guys i think lol.