They say this trailer was briefly posted to GameTrailers and captured before it could be hastily retracted. They say it shows off the story of Assassin's Creed III's multiplayer mode. They say you better look at it quick before Ubisoft has six kinds of legal fits and yanks it.
It seems quite likely GameTrailers might have a multiplayer preview for the anticipated sequel, and as Eurogamer points out, the footage includes snippets of development tools, which is an excellent explanation for why it might have been pulled.
In case it does vanish forever, the trailer includes a voice over speculated to be Abstergo's Warren Vidic, and is framed as a pitch for the commercial version of the Animus.
The new Wolf Pack multiplayer mode is shown, along with Wanted, Manhunt, Artifact Assault, Team Deathmatch and Capture the Flag.
There's also mention of a Story Quest section where players can unlock plot sections as they level up.
Assassin's Creed III launches at the end of October on PlayStation 3 and Xbox 360, is expected on PC by the end of the year, and is probably coming to Wii U, too.