You will need KB-3138612 and SUR Tool. Disconnect from Internet. Reboot, stay disconnected. Install the update. Restart. Install the SUR tool, it may take a while. Restart. You may now connect again and everything should be fine.

Source: the second answer with 66 votes at the time of writing this on the superuser forums.
http://superuser.com/questions/951960/windows-7-sp1-windows-update-stuck-checking-for-updates