The tool, known as a key generator, can be used to produce the random alphanumeric keys that are needed to activate the software upon installation.
The arrival of the key generator was noted in a posting by Microsoft enthusiast site Neowin.net earlier in the week. However, the group withdrew the listing for an undisclosed reason.
According to a Neowin principal, who asked to be identified as Creamhackered, the key software appeared to originate from China. It generates keys for both volume license and standard editions of several Microsoft products, including Windows XP Professional, Microsoft Office XP and Windows Server 2003.
"It takes less than a second to generate a key, and you can generate as many as you like," he said.
A Microsoft spokesman on Thursday said the company has the ability to differentiate between valid and invalid codes when customers contact the company for support or other help.
As a result, he said, officials at Microsoft, based in Redmond, Wash., are not overly worried about the implications of the most recent leak.
"From the Microsoft end, this just isnt that big a deal," the spokesman said. "In the piracy game in general, its a cat-and-mouse game. Microsoft expects to get these broken."
The activation keys were created as a way to prevent software piracy, and Microsoft has been a major advocate of the system. After installing a product, users must enter the activation code, which is then sent to Microsoft for validation. The idea was to prevent customers from installing the same copy of a product on multiple machines.
But this is by no means the first time that an activation code has made its way into the public domain. There have been several other such incidents in the past few years. Most recently, a key for Windows Server 2003 hit the Internet several weeks before the official release of the product in April 2003.
Microsoft is working on modifications to this system for the next major iteration of Windows, known as Longhorn, which is due in 2006. Activation keys still will be part of the equation, but some changes to the process are coming as well.
David Morgenstern of eWEEK.com contributed to this report.