Microsoft is suing a group of hackers who it claims gained access to the company's proprietary digital rights management source code and created a program that wipes media files clean of file-sharing restrictions.

The suit, filed in Seattle, gives only a nickname for the ringleader, "viodentia", who is one of 10 "John Does" whom Microsoft believes are responsible for breaking its Windows Media Digital Rights Management (DRM) software.

Last month, a program called FairUse4WM surfaced that removed the DRM technology from Windows Media 10 and 11 files. Many major download services, such as Napster use Windows DRM and its removal would allow the files to be copied without restriction or uploaded to file-sharing networks.

Microsoft is suing for copyright infringement, since FairUse4WM uses code from the company's Windows Media software development kit version 9.5, a toolset used by software developers to build applications.

Microsoft said the hackers have caused it more than $75,000 in losses. It is seeking a permanent injunction against the defendants and compensation.

In a separate document filed with the court, Microsoft said the defendants have gone to substantial lengths to hide their identities. It asked for extra time to issue subpoenas to email service providers, to track down some email addresses linked to the individuals, to help it to identify them.

The hackers have proved enduring foes for Microsoft. Soon after FairUse4WM was released, Microsoft issued an update to its DRM software, making the hacking program ineffective. The hackers responded less than a day later by updating FairUse4WM a second time.

Their efforts are unlikely to affect the growth of legitimate download services, however, since content providers are aware that no DRM is unbreakable, analysts said. "I think in the long term it's not going to deal Microsoft any crushing blow, but it's certainly an irritant for them," said Jonathan Arber, research analyst for Ovum.

Technology companies will have to make it too hard for hackers to break the DRM, a leap that could be difficult considering any update to the DRM technology would still have to be compatible with hardware in the market, said Paul Jackson, principal analyst at Forrester Research.

Additionally, frequent software updates tend to alienate users, he said. "It’s a question of highly determined hackers desperate to prove themselves, versus a corporation that can't release updates every 10 minutes because that annoys people," Jackson said.