These people should be brought in front of justice and exchanges can do it very well by collaborating with one another. That is good part of hearing loss in BNT has been recovered by freezing the tokens. Bancor team has taken bold decision by putting the actual situation in front of people instead of hiding the incident and this is great thing.
thats what exchanger should do collaborate with each other to avoid breaches and prevent the thieves from liquidating the stolen tokens, but tracing transaction will be hard bancor can ask etherscan to flag the address involve in the breach.