Its not a violation to play more than one character at once, this guy is talking absolute shit. Report him/her for harrassment. Also if they believe that they can get "keyloggers" from visiting a website they are pretty damn noob at computers.

But yeah, having only two of the accounts registered in your name is probably not a good thing. Blizzard are fairly strict about that, so I'd get into contact with them ASAP to clear it up, try and get a dialogue going between them and the original owner to sort it out as this is the sort of thing which might come back to bite you if left unchecked.