It's not impossible of course, but I believe that the hacker attacks have caused limited damage. The main reason is that MtGox only allows 100 BTC withdrawals per day. Each unsuccessful withdrawal takes a week (before the balance is returned). This started two weeks ago and MtGox got warned early enough and took countermeasures before everything got out of control. This is the reason why they frozen all BTC withdrawals. I believe they'll be able to clean up everything, but it will take some time. It's certainly a very interesting situation. There are multiple different problems that magnifies the situation. Again, other exchanges could suffer from the same problem. As far as I understand, all the exchanges are currently being contacted and warned about the current situation.