Microsoft is investigating how code for unreleased shooter Halo 4 has made it onto the internet.
The company says it is working closely with law and security agencies to try and track down the source of the leak.
Fans of the series are being warned to avoid the many unofficial videos doing the rounds that spoil some of the narrative surprises included in the title. And Microsoft is chasing the people responsible for those, too.
"There are people putting the whole thing on YouTube," Halo franchise director Frank O'Connor told Polygon. "Microsoft is addressing that a single case at a time, it just takes a little while to handle."
When asked for his reaction to the leak, O'Connor shrugged slightly and said this is how surprised I am about this”.
Microsoft has confirmed that it will not alter its launch plans in light of the news.
Halo 4 is due out on November 6th.