The Halo: Reach code leaked over the weekend is now being circulated and illegally downloaded from torrent websites.
The game, which is slated for a 14 September release, was procured by hackers who managed to break past security on Xbox.com and stole the full game code meant for game reviewers only.
According to tech news site PC Mag, the leak was made by a forum group dubbed GameTuts.
PC Mag suggests that some of the blame for the leak must lie with Microsoft, which decided to share the final code with developers just few weeks before the official launch.
The leak will probably not affect the popularity of the game, nor its sales figures, however. When Microsoft had decided to launch a beat preview version of the game, as many as 2.5 million Xbox gamers had participated, suggesting at future sales success.
Microsoft has announced that it has launched a full scale investigation to catch those responsible.