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Spent a lot of time chasing security phantoms, had a nap and had an epiphany, a user had brute-forced their own account. Fuck knows why they do stuff like this, and double fuck knows why they then say nothing.
Of course in certain societies face is a very big deal, and you'll get nowhere because of it.
You never make the accusation of course, you just lay out the evidence that makes it obvious and hope they say something. I wouldn't even be mad, I just don't like having my time wasted.