Halo 4 Xbox pirates targeted by Microsoft
Microsoft is targeting video gamers playing pirated copies of its forthcoming title Halo 4.
Several users have already had their Xbox Live accounts "permanently suspended", preventing them from being used to access multiplayer games via the internet.
The firm has also indicated that some might face tougher punishments.
The latest Halo game is not due for release until 6 November. An early leak of its code threatens to limit sales.
"We are aware of isolated cases in which Halo 4 content has been propped on the web and are working closely with our security teams and law enforcement to address the situation immediately," Microsoft said in a statement.
"Consumers should be aware that piracy is illegal and we take vigorous action against illegal activity related to our products and services."
Although there is nothing to prevent users with blocked accounts from creating new ones, Microsoft has said it might also enforce "console bans" designed to permanently prevent targeted machines accessing its network.
Halo 4 is being marketed for about £50, although many retailers plan to sell it at a cheaper price at launch.
News of the action was first reported by the video game trade magazine MCV. It reported that a version of the game was first leaked on to the internet over the weekend, allowing others to copy and play it.
That in turn has led to video clips of the title being posted online, spoiling some of the product's surprises.
"The Halo 4 leak has happened much earlier than these things normally do, and the fact is that many people are going to want to play it," MCV editor Michael French told the BBC.
"Piracy is a bit of an unspoken force on the Xbox 360. The industry talks about it being rife on PCs - which it is - but it also exists on consoles.
"A modded machine allows you to download the files over the internet and play them yourself. It's not super-hard to do but it is illegal."
In the past it used to be difficult for publishers to track such activity.
But playing with or against others via the internet is now part of many games' appeal, and when a user first connects to a console-maker's servers after launching a new title it can carry out checks on the software.
A study by the Entertainment Software Association of Canada has suggested video games piracy accounted for 3.5bn Canadian dollars (£1.6bn) worth of lost gaming sales a year in the US and Canada.
Publisher Ubisoft also made headlines earlier this year when it said it believed up to 95% of the versions of Assassin's Creed, Driver and other of its games played on the PC platform had been pirated.
"One of the most effective ways both the console industry and PC market - through systems such as Valve's Steam facility - are trying to combat this is by building up a gamer's online identity," said Ed Barton, director of digital media at Strategy Analytics.
"That includes creating a friends list and achievements.
"The threat of having this taken away can be just as devastating to a gamer as losing their Facebook account."