Blogcritics reports many Halo 3 owners are missing major chucks of their Halo 3 Service Records at Bungie.net. The Service Records contain every Halo 3 player's kill and death counts, experience, rankings, medals, and other achievements earned from multiplayer games. Many players have not had their Service Records updated since Thursday, October 4. Others have not had an update since September 30, a full week ago.
Halo 3's online matchmaking service was being reported as down as well, and it is unknown yet if the two problems are related. However, the problems do not seem to be affecting all Xbox Live users. Bungie has not yet addressed multiple complaints in its official forums.