All exchangers have their own security measures, all of them are very secured so its safe and reliable But i still recommend you to have your own digital wallet, so if ever something bad happens to the exchange your coins will be safe as long as you dont lose your private key.
You're right. No matter how secure the exchange is, there are hackers that one day will break their security and steal the money. It is possible. As well as wallet hacking is possible. We need to split between wallets and exchanges.