I'm betting it's pirated copy that's using 7Loader by Daz or a similar activator. On final reboot, it installs an OEM certificate and serial (key), and modifies the boot code to boot a modified GRUB that loads an OEM SLIC (that normally resides in the BIOS) to the appropriate location in memory, so that Windows will see it as if it came from the BIOS. Ta-da! Windows is "activated", because the certificate, serial, and SLIC all match, let's say, Acer's. M$ can't block the key or all Acers will go dead. That and 7Loader has certs, serials, and SLICs for almost every major manufacturer, with the ability to add your own if you want.
EDIT: Well, I should mention, the only difference between an activated copy that uses a loader and a genuine copy is the fact that M$ doesn't get paid any money for it. Unless, of course, someone also included a virus, keylogger or what-not with it, that's always a possibility, but that's apples and oranges. A pirated copy activated with 7Loader isn't detectable by M$ (unless they manage to check the boot code, which would be hard because 7Loader inserts random code into every activation).
