REDMOND, Wash., Feb. 12, 2004 -- On Thursday, Microsoft became aware that portions of the Microsoft Windows 2000 and Windows NT 4.0 source code were illegally made available on the Internet. It’s illegal for third parties to post Microsoft source code, and we take such activity very seriously.

We are currently investigating these postings and are working with the appropriate law-enforcement authorities.

At this point it does not appear that this is the result of any breach of Microsoft’s corporate network or internal security.

At this time there is no known impact on customers. We will continue to monitor the situation.

Source: Microsoft

Two words. Yea, right.

Didn't MS decide to show certain portions of the Windows source code to Key Custommers in order to write software optimised for that platform ?

I'm thinking the leak might be from one of those key customers.

& BTW is it the complete source code to these OSes or just parts ?

They're not sure what's got out there yet supposedly, though they don't believe it was the full source code anyway. I guess it depends where the code came from until we know what portion's been released.