In a deal naming almost no specifics, Bungie Studios, a wholly owned unit of Microsoft's Microsoft Games Division, becomes the privately held Bungie LLC, with minority Microsoft shareholding and a long-term Halo publishing deal.

http://www.bungie.net/News/content.aspx?type=news&cid=12835

Bungie spent slightly more than seven years and fifteen weeks owned wholly by Microsoft, releasing four games during that period: Oni, Halo 1, Halo 2, and Halo 3. Halo 1 and Oni underwent significant development before the purchase.