Microsoft says it's investigating a wave of permanent matchmaking bans being dished out to Halo 4 players.
Many affected players claim that downloading Halo 4 DLC the Crimson Map Pack has resulted in them being banned from certain portions of the game's online component.
A moderator for 343 Industries said last night on the Halo Waypoint forums: "We are not permanently banning players for previewing or purchasing the Crimson Map Pack. We are currently investigating the recent reports of permanent matchmaking bans.
"We will provide further updates tomorrow. Thank you for your patience."
Halo 4 sold around four million copies in its first month of availability, helping lifetime franchise sales reach 50 million units.
Our Halo 4 review described 343's debut series entry as "one of the best multiplayer shooters on 360", although we said "Reach has the better Firefight and Halo 3 has the better campaign".