Microsoft has since taken down most of the spoiler-filled gameplay footage from leaked copies, though some videos can still be found on YouTube at this time.
Microsoft has also responded by issuing permanent Xbox Live bans to any users found online playing a leaked copy.
Developer 343 Industries is apparently unsurprised by the leak, as the game's director Frank O'Connor told Polygon: "There are people putting the whole thing on YouTube. Microsoft is addressing that a single case at a time, it just takes a little while to handle."
He added: "This is how surprised I am about this," and shrugged.
Halo 4 is set four years after the events of Halo 3, marking the return of iconic hero Master Chief and representing the beginning of a brand new saga.
In addition to the single-player campaign, Halo 4 will feature a robust multiplayer offering through War Games, which will take place on the Spartan training ship Infinity and will tie into the game's story.
343 Industries recently announced that there will be downloadable class specialisations available for multiplayer, as well as a War Games Map Pass providing access to future DLC maps.
Named 'Best Shooter' and 'Best Multiplayer' during Digital Spy's Best of E3 2012 awards, Halo 4 will be available exclusively on Xbox 360 from November 6 worldwide.
> Halo 4: Forward Unto Dawn Episode One review: Live action series debuts
> Halo 4 preview: Master Chief's return feels both old and new
Screenshot gallery - view Halo 4 images below:
Copyright: Microsoft Games