Over the past years I've aquired different windows 7 x64 versions on Disc, both ISO burnt to DVD and the discs I got with my store-bought laptop. Being an obsessive compuslive guy who needs to know everything I'm now obsessing with figuring out the authenticity of my discs. The W7 Home edition DVD's that came with my laptops are no biggie. Two other ISO's I aquired through MSDN for work back then as db-analyst are fine as well and SHA numbers match with the ones on MSDN. However I got 1 disc I copied to disk and the SHA1 numbers don't match with any on MSDN.I understand Win 7 ISO's can be modified. All Discs actually contain all different versions. Modifying just 1 small configuration file to install any version, could therefore have changed the whole checksum for the ISO. Meaning if the checksum doesn't match any on MSDN it doesn't mean it's not legit. My question is if you could all help me figure out what might have been changed this ISO to make it have an "unofficial" SHA1 number. I hope to learn about windows7 installation discs as well. Here's the information for this 1 disc: directory dates: 7/14/2009/11:29 size on disc: 3,224,686,592 iso size: 3,224,698,880 SHA1: c162759fb80c07f93ad3e28ca307a3aee5c52715 Windows Media-player seems not to install automatically with this version, so it could have been removed or opted out though a configuration file that has been modified. Do not know if mediaplayer could have been removed entirely. Not sure. Any other options also possible. What should the next move be?