For now all exchange that i used is centralized , i been use this exchange since acouple years and untill now i never get any problem. I know some centralized exchange was hacked but i have seen also decentralized exchange of Etherdelta been hacked too about 1 years ago, and also Bancor decentralized exchange also hacked a few month ago.
Whether it's centralized or decentralized, one should always be careful when accessing those exchanges. There are so many phishers out there and when you think that you are already safe and be lax when doing trading or when you go to their site when searching google then you should carefully scrutinize if that is the right site. You should bookmark it always so that the next time you visit it, you don't need to search for it.
To minimize the risk of exchange is we should be use more than 1 exchanges. I hope decentralized and centralized exchange increase the level of security so no more hack in crypto exchanges.
Aside from using more than one exchange, you should also put only your funds in an exchange if you need it to be there always and take advantage of the opportunity of fluctuation. Otherwise if you are a long-term investor of the coin which may take years before you sell it then put it in your wallet wherein you are the only one who can access it. Being it there in the exchange has the higher risk of being hacked.