A leaked build of Windows 8 has hit the internet. The beta forum BetaArchive has one of the first records of the release, which was uploaded by an anonymous user (of course).
The file name for the 2.45 GB image is 6.1.7850.0.winmain_win8m1.100922-1508_x86fre_client-enterprise_en-us.iso.But it's a fake. (see update below)
Slyck read the feedback from torrent sites and found comments saying that this is just Windows 7 renamed to Windows 8: "This is a fake. Info gathered from files : 6.1.7600. 16385(win7_rtm.090713-1255). Since Win 8 is a new kernel, this aint it."
UPDATE: Slyck may be incorrect. This could really just be an old, but genuine build of Windows 8.