Larry Hryb, who goes by the online handle "Major Nelson", confirmed the news with a post Thursday on his blog. Halo Reach, according to Hryb, is now the most frequently played game on Xbox Live.
It's followed by Call Of Duty: Modern Warfare 2, which held the top spot for several months, and Halo 3 in third place.
Rounding out the top five are Call Of Duty: WaW, and FIFA Soccer 11 (demo version). FIFA 10, Call of Duty 4, Madden NFL 11, GTA IV, and Red Dead Redemption rank fifth through tenth, respectively.
Microsoft and retail partner Best Buy held launch parties earlier this month in New York, Seattle, and London, England to mark the game's release. At the New York event, crowds lined up for blocks around the city's famous Times Square area to be among the first to purchase the game.
Halo Reach, an Xbox 360 exclusive that was produced by Bungie, is billed as a prequel to the original version of Halo. "Halo Reach follows the story of Noble Team, a squad of heroic Spartan soldiers as they make their final stand on planet Reach, humanity's last line of defense between the terrifying Covenant and Earth," according to Microsoft.
The game comes in three editions—a $59 basic version, a $79 Limited edition, and the $149 Legendary edition.
Microsoft is also hawking a $399 bundle that features a Halo-themed, 250GB Xbox 360 console and wireless controller, as well as the basic edition of the game, Halo Reach features a new graphics and audio engine that offers enhanced visuals and sounds over its predecessors, Microsoft has said.