I don't know that this is a bug report so much as it is a hacking report, so maybe it shouldn't be here. I have been adding members manually to a site, as I've been selling memberships off another site. Added a bunch in a few days ago, then was back in today, and saw a very strange name in there - one that I had not put in, nor was I paid for.
I have screen shots, whatever you need if you're interested.
Patricia