Indeed, this is a real concern.

However, no system which relies on a password scheme to limit entry is safe once the password is compromised. Once you have passed all password-controls, you are essentially free to do as you please (or the system allows you to do within the privileges granted to you by your current access-level). Simply (or naively) adding additional passwords (or public keys, ...) only transfers the problem one level further: What happens if this password, ... also gets compromised, lost, forgotten, invalidated, ...?

Your posting however begs another question: have any PM-accounts been compromised or stolen from their rightful owners?