lentinman: if someone gained access to your brokerage account they could sell all your holdings with market orders and plow the proceeds into a low float stock(s) which they owned a sizable position in. Effectively they'd be transferring capital from your account into their's.
I've never heard about anything like that happening, but it's a scary thought. And depending on the trades, it might not even be that easy to catch the crooks or prove they did it !