The Internet was abuzz this weekend with word of a Halo 4 leak, and warnings to steer clear of spoilers. But it also had the inadvertent effect of raising questions about a purported second disc. Microsoft has stepped in to clarify that it contains multiplayer install data.
Microsoft told Joystiq that the second disc is a required install, which will need at least 8GB of memory to play Halo 4's "extensive suite of multiplayer features." Presumably, this will include both traditional competitive multiplayer and the new co-op Spartan Ops campaigns. Once the second disc is installed, you can just keep the first disc in the tray instead of swapping them out.
This comes amid reports that Microsoft's internal security team is working with law enforcement to catch the source of the leaks. Microsoft has reportedly started permanently banning pirates from Xbox Live.