Halo 4. Pirates are now receiving emails explaining the situation, reports MCV. The emails note that the user in question has been "permanently suspended for illegitimate prerelease title play." Lest the word "permanent" be unclear, the email goes on to note that "Xbox Live privileges will not be reinstated." Microsoft pursued a similar course of action prior to the 2010 release of Halo: Reach.
It's worth noting that the email refers to Xbox Live "account privileges," which may indicate that Microsoft is banning user accounts but not the actual console on which they reside. In such cases, users can regain access to Xbox Live by starting a new account (which means paying for a new account in the case of Xbox Live Gold). We've reached out to Microsoft to find out if consoles are being banned as well.
Microsoft acknowledged reports last week that Halo 4 had been leaked onto the internet, and that it is "working closely with its security teams and law enforcement to address the situation."
Update: Microsoft has responded to Joystiq, reiterating its stance. While it wouldn't confirm if all Halo 4 pirates will receive full console bans, it did confirm that both account and console bans may occur.