It's simple. If I had a login to your account (or guessed the password correctly), I could do exactly that.
It's not like we've never had dopplegangers on accounts here before.
Actually more bizarre is a friend of my wife's who had problems with FB and Yahoo with someone who took over someone's login and started doing credit card fraud type stuff. Apparently the woman's husband tried to clamp down on it, and within a week the guy was murdered. Pretty freaking trippy.