The screenshots giving details about the Windows 8 Build 7900 has been leaked and seems to be genuine. The first screenshot is of the setup file of Build 7900 and the second screenshot shows the Digital signature which confirms the that the build is genuine. These screenshots states that the build 7900 has the old Kernel i.e 6.1 and was compiled on November 8, 2010
The complete build string is 6.1.7900.0.101108-2111 .We are regularly updating our Windows 8 build lists,you can check them here
Update: According to our sources this build is confirmed to be fake..