As anticipation that Microsoft may use its PDC conference in September to debut the first public beta version of Windows 8 increases, it appears that an old M1 build of the operating system is sailing the high seas.
Build 7850 - compiled on September 22nd, 2010 - has expired, yet is currently percolating through the usual sources.
An image from the aforementioned build, shows sparse UI differences to Windows 7. There's certainly no appearance of the ribbon interface expected to be part of the Windows 8 UI, but with the OS apparently nearing M3 status, it's reasonable to assume that current builds have probably taken on more of the essence that Microsoft is aiming to deliver with its next OS.
It is suggested that if the first public beta of Windows 8 does make an appearance in September, general availability could be pencilled in between Q4 2012, and Q1 2013.