1. "We got hacked" e.g Mt.gox
2. They actually get hacked
It's no secret that when the price of BTC increase , exchanges and other services becomes a target for hacking and sometimes It's actually an inside job where they claim they got hacked and of course , we can't proof it.
So to avoid any kind of regrets If that happens , I really recommend everyone to withdraw his funds from exchanges for the moment as we are heading to 1000$ pretty soon probably. Once you finish trading , just withdraw as there is no reason to keep them there... when you want to trade again , just deposit the amount to trade with and nothing more.
Exchanges that holds most of the funds in cold storage could be more secure but you never know... so yeah , be careful.
It's really possible at this point especially the price is surging up. If that kind of things is happening everytime there is a price increase, what's more now because it's really close to $1000 mark which is highly a long time desire for any bitcoin users.
But you know even there isn't a price increase rally that is happening, people should also study on how they will deal with the security of their bitcoins without using web exchanges.