It never asked me for username (in fact I don't have a Microsoft account), I find it so annoying, I always turn on the PC and that's it, but now since saturday it asks me for an username in order to log. I didn't edit system related stuff, never touched the Netplwiz thing or anything like that, so it's kinda weird.
What could it be? a virus? hack? or something else no need to worry about?