They know how to secure their exchange its just hackers became more smarter than them that's why we see this hacking issues existing even if the exchange spend a lot of money for security measures. What's important matter there is we choose a big exchange when trading so that if this incident will happen to them they can give some assurance that no investors funds will get affected and all users can still access their funds without any issues.
Not only Houbi encounter such unfortunate attacks but rather also those top tier exchange like binance but what good happened there is they still standing strong and can able to operate even if issue like this happen to them. Its important for trader to be aware on this situation so that they may know on what to do next if situation like this might occur in future.
Exchanges will always experience increased risks due to their type of activity, they will always have vulnerabilities and hackers will try to repeat their attacks. To some extent, along with the increase in security, the capabilities of hackers also increase and it is impossible to take everything into account, sometimes protection can only be strengthened when you see where the vulnerability was.
In fact, I don't know if there are any exchanges that have never been hacked. What is important here is how quickly the defense service can react so that losses are minimal.