In connection with the last Ddos-attak on the EXMO exchange (the official response of the exchange), it is a question of time who will be the next target.
You're asking questions that its like we are nostradamus or we are those bastards that will attack a website for ddos.
There are lots of paid tools/services that fights for it, tho it cannot prevent from happening at least it minimize its damage.
If you're worried of who will be the next target exchange of hack or ddos. Then probably you should diversify your trading funds to at least 3 trusted exchange.