Actually, unknown user can also mean that the account has been deleted. And from what I’ve seen, Medium has been doing a pretty good job doing just that with these opportunists.

For some reason, I’ve had a whole rash of comments in the last couple weeks that were really just spam, and often for snake oil or something nefarious.

I’ve reported them, and I’ve seen the accounts deleted fairly quickly if not instantly.

This type of thing does seem to be happening more lately. I suspect a person or group of people have hit upon the idea as a good marketing method for their scams.