I think if hacking compromises the exchange, you’d want it shut down.
It also tells you to keep your bitcoins downloaded to your own thumb drive.
Now is that safe? I don’t understand the algorithm well enough to know.
As I understand it, each bitcoin (or fraction thereof) has a code. Surely the owner of the coin has to report to the ledger that the coin is being taken out of circulation.
Couldn’t a hacker report to the exchange that it is being put back in circulation, and then spend it?