While not the full game (impossible, since it's not even done yet), some enterprising thieves appear to have managed to get hold of a demo for the upcoming Call of Duty: Black Ops 2. And proceed to do what you'd expect.
Namely, we get a video with the worst soundtrack on Earth, obnoxious overlays of developer interviews and obtrusive watermarks.
While the demo - presumably lifted from a recent Black Ops II's showing - is only limited to a bit of multiplayer, Activision has since confirmed to Kotaku that it's a legitimate portion of the game, issuing a statement that reads "The video posted is from a development demo build, using developer tools meant for testing. The retail build was never accessed or compromised."
Which explains all the jumping and floating around; while the video was first posted on the YouTube page of a self-professed Call of Duty modder, and is angled as some "triumph" for hackers, Activision's statement suggests the "no clipping" visible is the result of "developer tools", not a hack or mod.
UPDATE - Story edited to reflect Activision's confirmation.
UPDATE 2 - We've heard the leak may have come from a closed internal beta, not a public showing.
iHcJames [YouTube, original video removed]