Right, the whole data.dat thing seems to be a bit of a concerning mystery. I've obtained a couple of these files and binary compared them; none have been the same size, here's where it stands so far: ambidav: 18kb - unknown creation method FaiKee v1: 24kb - unknown creation method FaiKee v2: 24kb, installed and activated with KMS, changed to MAK key and reactivated, Pro WMC applied and activated Mine: 16kb, installed and activated with upgrade retail key, WMC key applied and activated Now the interesting thing is that whilst the majority of the file is completely different (I assume encrypted based on HW ID), there are common markers between mine and ambidav's file. The odd thing is, his is 2kb longer. What I'm looking for, from you guys, is your self-created data.dat files, along with details of your creation scenario. I want to find out if there's a specific difference between KMS installs, MAK installs, upgrades from Windows 7, and Core --> Pro --> WMC scenarios. The purpose of this is to determine whether or not Microsoft would be able to detect exactly what method you'd used to activate, and revoke your activation in future if using an "unsupported" method (ie, one that goes against the EULA). If you could attach your data.dat to this post, that'd be brilliant. Cheers! Updates: 04/11/2012, 09:32 - FaiKee posted a second version of his data.dat, apparently the first was from his friend; this, too, is 24kb and was MAK-activated. This file, again while being largely different from the first 24kb version, has common markers in the hex throughout the file all the way to the end. If someone else with a MAK-activated + ProWMC setup could post their data.dat, this would go a long way to confirming a 24kb data.dat for MAK copies. 04/11/2012, 12:15 - Just did a fresh install using KMS activation, 11kb data.dat; applied WMC key and installed without activating, data.dat became 15kb. Now testing the installation of WMC using the public WMC key, and will check the size and then test that in a slipstreamed ISO to see if that allows installation and activation using the free WMC key. Overall, this seems like the safest way, as it doesn't tie you to any identifiable issued key, retail or otherwise.