I believe you can view any coins that are in the process of unstaking. For example in my wallet, I'm in the process of unstaking and because of that I cannot use the CPU and RAM of coins that are being unstaked. I think that an exchange would notice any hacker trying to unstake a coin and would then go onto re-stake it. They could then change the private key or also ask BPs for assistance.
RE: Exchange hack of EOS is IMPOSSIBLE!! | Yes Impossible