While pursuing those responsible for leaking a preview build of Deus Ex Human Revolution onto the internet, publishers Square Enix discovered that the game (well, part of the game) had been a copy they'd hosted on Valve's Steam service.
This happens all the time; often with PC preview coverage here at Kotaku, for example, we're able to access and download early builds of games on Steam.
The problem here is that an Italian writer's login details were obtained by hackers and Deus Ex's code lifted, then leaked.
Valve says that it has a lot more information on those responsible than it's released thus far, but also says it's unable to give that information to Square Enix (courtesy of its privacy policy) unless the publisher can present them with a subpoena.
So Square Enix is doing just that, asking the Washington court hearing its case against fifteen unidentified Italian hackers for permission to get just such a subpoena.
Subpoenas! Shady European criminals! It's like a cop show! Only, with paperwork instead of guns.
Square Enix Files Suit Over Deus Ex: HR Leak, Valve Caught In Middle [Gamasutra]