SEATTLE - Microsoft Corp. said late Thursday that portions of its Windows source code — the tightly guarded blueprints of its dominant operating system — had been leaked over the Internet.

Microsoft spokesman Tom Pilla said in an interview with The Associated Press that some incomplete portions of the Windows 2000 and Windows NT4 source code had been "illegally made available on the Internet."

Access to the source code could allow hackers to exploit the operating system and attack machines running Windows, which is used on hundreds of millions of computers worldwide.

The company was made aware of the leak on Thursday and is investigating, Pilla said. He did not know how much of the code had been leaked or how many people may have gained access to it. The company could not immediately pinpoint the source of the leak, and has contacted law enforcement authorities, he said.

Pilla said there was no indication the code leak was a result of a breach of Microsoft's corporate network. There was no known immediate impact on Microsoft customers, he said.

Microsoft has previously shared some of its source code with some U.S. government agencies, foreign governments and universities under tight restrictions that prevent such organizations from making it publicly available. But the company has generally argued that the blueprints to its operating system are proprietary, and shouldn't be made public.

Still, because some people outside Microsoft have had access to the code, analysts said it wasn't too surprising for such a leak to occur at some point — either intentionally or unintentionally.

"It seems unlikely this is going to create a material, significant security problem, said Rob Enderle, a technology expert and principal analyst with the Enderle Group. "It's more embarrassing than anything else because it makes it look like Microsoft can't control its code."

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