If they had spend costumer deposits making the amounts on peoples accounts not backed by real money and BTC, then yes, but that could have been going on for months on the way up without anyone knowing. So if that's the case, your money could have been stolen weeks ago, not today. they would have used new $$ deposits to pay the ones cashing out until they started to pay out more out than they got in, a real ponzi.

However that would still be fraud in the real world taking peoples money in a scam. Dealing in Bitcoins does not protect the owners of an exchange from the law.

that has never happend in an exchange, true, but in numerous other Bitcoin "businesses" around here.