Ubisoft have released the multiplayer DLC pack, The Hidden Secrets, for players with an Assassin's Creed III season pass. The pack contains two new playable characters as well as three maps (Lost Mayan Ruins, The Ghost of War, and A Dangerous Secret).
If you haven't got a season pass you'll have to wait until next week (PC/Xbox 360 - Dec 11, PS3 - Dec 13) for the privilege of buying said content.