BetaNews has learned that originated not from Microsoft, but from long-time Redmond partner Mainsoft.
The leaked code includes 30,915 files and was apparently removed from a Linux computer used by Mainsoft for development purposes. Dated July 25, 2000, the source code represents Windows 2000 Service Pack 1.
Analysis indicates files within the leaked archive are only a subset of the Windows source code, which was licensed to Mainsoft for use in the companys MainWin product. MainWin utilizes the source to create native Unix versions of Windows applications.
Mainsoft says it has incorporated millions of lines of untouched Windows code into MainWin.
Clues to the source codes origin lie in a "core dump" file, which is left by the Linux operating system to record the memory a program is using when it crashes. Further investigation by BetaNews revealed the machine was likely used by Mainsofts Director of Technology, Eyal Alaluf.
References to MainWin can also be found throughout the leaked source files, which do not compile into a usable form of Windows.
Prior to Microsofts Shared Source Initiative launched in 2001, Mainsoft, which calls itself "the software porting company," was one of only two partners with access to the Windows source code under Microsofts Windows Interface Source Environment (WISE) program.
The goal of WISE is to enable developers to write applications using Windows APIs and deploy them on Unix operating systems such as Linux.
Mainsoft extended its WISE agreement with Microsoft in March 2000 to include access to the Windows 2000 source. Microsoft subsequently employed Mainsoft to port Windows Media Player 6.3 and Internet Explorer to Unix.
Although the leak poses a serious threat to Microsofts intellectual property, its limited scope is sure to help the company alleviate fears of potential disaster. Microsoft has opened an investigation with the FBI and says its internal security in Redmond was not affected.
Because Mainsoft used only select portions of the Windows source for MainWin, Microsoft may find itself more worried about the egg on its face than possible exposure of its flagship operating system; Windows 2000 served as the foundation for Windows XP and Windows Server 2003.
It is not clear at this point how the three and a half year-old source code escaped Mainsoft.
Eric Steil and David Worthington contributed to this report.