Of course - in the past, I think many accounts have been hacked and then sold. Old accounts are hacked for various reasons - others have been sold by their original owners and the new owners use them to join signature campaigns. There have been many such cases till now and most of these accounts cannot prove ownership like signing bitcoin messages.

Highly ranked accounts are most often targeted for hacking because the higher an account's ranking the hacker can sell it for a higher price. Not sure someone would hack a newbie's account if they themselves can create dozens of other newbie - unless the newbie clearly tells someone has a lot of btc that will provoke the hacker to find out a lot of information from him.