Microsoft has confirmed that a pirated copy of Halo 2 for Xbox in the PAL video format and French language started circulating on the Internet late Wednesday night.

It's thought the game was 'leaked' from a European manufacturing plant used to press game discs. Microsoft is threatening legal action against those making the game available for download.

"We consider downloading this code, or making it available for others to download, as theft," said the company in a statement. "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."

As one of the most successful franchises on the Xbox, the leak of Halo 2 on the net presents serious concerns for Microsoft, which expects high sales when the game launches on November 9.