I bought a new PC last week (assembled myself, i.e. no prebuilt PC). I installed Linux Mint as the first OS, today I installed Windows 10 on a separate harddrive (which I used before in a Linux notebook). To the best of my knowledge no piece of hardware I use in this PC has seen a Windows OS before.
I checked the "I don't have a key" option during installation, planning to activate Windows afterwards. However, it appears to be already activated (with a digital license and a retail version). Executing slmgr/dli in cmd gives me "3V66T", which sounds suspiciously like the default key for upgrades from earlier Windows versions.
My questions: How is it possible for my Windows OS to be activated without providing any key? Am I missing or misunderstanding anything? Also: Is it any security risk if my Windows installation is activated by an unknown source?
