Microsoft is investigating how one of the most hotly anticipated Xbox titles of the year appeared on the net three weeks ahead of its official release.

Halo Reach, due to be launched on 14 September, appeared on file-sharing sites such as The Pirate Bay. Within hours of being available, videos of the game began to appear on YouTube.

The first-person shooter has already been downloaded hundreds of times.

Reports suggest that the leak occurred after the game was made available to select reviewers and journalists via Microsoft`s online Xbox store.

"We are still investigating details surrounding a claimed leak of Halo Reach and have nothing further to share," Microsoft said.

BDST: 1655 HRS, 24 August 2010