Microsoft has confirmed that some of the source code for Windows 2000 and Windows NT has been leaked onto the internet.

Web forums were ablaze with the rumour late last night, after postings on Slashdot and Neowin claimed that files appearing to be Windows source code had shown up on peer-to-peer programs such as BitTorrent.

Microsoft later confirmed the leak, but denied that customers were at risk.

"Microsoft became aware that portions of the Windows 2000 and Windows NT 4.0 source code were illegally made available on the internet," the firm said in a statement.

"It is illegal for third parties to post Microsoft source code, and we take such activity very seriously."

The code is contained within a 203MB compressed file and is not complete. Uncompressed it fits on a CD, which could indicate plans for future mass distribution or simply the method by which it was stolen.

But the code will be useful for those designing malware to attack Microsoft's software. Sections of Windows XP are based on the NT and 2000 code.

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

The software giant has already launched an investigation into the posting and is working with the appropriate law enforcement authorities to find the source of the leak and to monitor possible future distribution.

"At this point it does not appear that this is the result of any breach of Microsoft's corporate network or internal security," the company claimed.

The relevant code has already been seen by governments and 50 universities participating in the Microsoft Shared Source Initiative, in which parts of the operating system code are made available to select developers.

This is not the first time Microsoft has had sections of its source code exposed. In 2000 some code was revealed after an employee working from home allowed hackers access to Microsoft's servers.