You don't get money for winning this game, do you? What kind of a sad, sad person feels the need to cheat at online games? I mean, all it does for you is make all the other players feel the mild disappointment of losing. If you're the kind of person who does something for the sole purpose of making other people feel bad, I'll bet you also go around throwing rocks at the homeless.
Anyway, it's pretty obviously a glitch. The date was supposed to be something like twenty days after today, but the programmer forgot to sign a variable and the date got set to negative twenty days. Which means the date got looped back around to twenty days before the last day, or 12/12/9999. Still funny, but not as much as if he was actually banned for 8000 years.