Never keep money on exchange - this is first gold rule in crypto. Always try to avoid this at all cost, no matter how long exchange is in business and how trusted they are. if I keep my money on my favourite exchanges: Mintpal and BTC-e today I will have nothing left. I didn't expect Bittrex to disable user accounts without any statement, it will impact their business badly.
Thats what i tell everyone. There is no Bitcoin insurance , and if a disaster strikes, no one will replace your Bitcoins. A bitcoin exchange can be made from a free and readily available script on GiHub. For security reason one can hire a certified security expert. That expert might hold only a certificate, if he is very talented he might be recruited somewhere else. He might wank few times a day.
In a scenario a worker is suspected of being steeling bitcoins, using only common sense, it is hard to prove that you have Bitcoins on you, and if you do really have them hidden somewhere it is almost certain that they are gone for ever!