An early build of Windows 8 from Milestone 1 in September of 2010 has leaked to FTP sites and Torrent sites. This is definitely an older build, and is not anywhere close to what to expect from Windows 8.
The build is currently being distributed on FTPs and file sharing sites after an anonymous leakster posted the bits to the beta archive site. The build is an early sample of Microsoft’s work with Windows 8 and does not reflect the current state of winmain builds. As the build was compiled in late September it has since expired and those wishing to experiment with it will need to turn their BIOS clocks back.