"We are currently investigating the source of this leak with the appropriate authorities. Microsoft takes the integrity of its intellectual property extremely seriously, and we are aggressively pursuing the source of this illegal act. We consider downloading this code or making it available for others to download as theft." - Microsoft.
Looks like Microsoft is taking the leak onto the net of Halo 2 pretty badly, and can you blame them? The game, which was a key title for Microsoft on the run up to Xmas, is now floating around in Usenet somewhere, if you can be bothered finding it and bothered with the 3GB download. This version has no multi-player support, but this will not alone be enough to dissuade IRC savvy netizens from getting their hands on the game for free.
Microsoft claims that none of this will make the slightest difference to their Halo 2 launch, which is due to take place in the second week of November. The game remains an eagerly awaited Xbox title.