Microsoft has enlisted the help of the FBI to track down the source of the leaked Windows 2000 and Windows NT source code.

The software giant said investigations have found that the code posted on the internet was not the result of any breach of Microsoft's corporate network or internal security.

Nor, it said, was the leak related to the company's Shared Source Initiative (SSI) or to its Government Security Programme, which enable universities, developers and governments to legally access certain parts of the Windows source code.

In a statement Microsoft said: "At this time there is no known impact on customers. We continue to be committed to protecting our customers and their networks, and we will take any appropriate steps to ensure that we meet this commitment."

Reaffirming its support for both the SSI and the Government Security Programme, Microsoft said it would be working closely with the FBI to trace the leak.

"Microsoft source code is both copyrighted and protected as a trade secret. As such, it is illegal to post it, make it available to others, download it or use it. Microsoft will take all appropriate legal actions to protect its intellectual property," the company said.

According to reports, the leaked code contains references to Microsoft partner Mainsoft.

Mike Gullard, Mainsoft chairman, said in a statement: "Mainsoft takes Microsoft's and all our customers' security matters seriously, and we recognise the gravity of the situation. We are co-operating fully with Microsoft and all authorities in their investigation."

Mainsoft has been a Microsoft partner since 1994, when the companies first entered into a source code licensing agreement.