This question is need and answers from the experts! But my opinion is differ from experts" According to the book I read No system is Perfect in the world and because of this No system is safe" I don't know if its true but i think those hacking incident can be avoided if doing a necessary action to pre-empt the possible hacking attack instead of relying the existing security protocols (ex. wallets that store large amount of cryptocurrency must put in offline if its possible) this is only and opinion and i'm not an expert regarding this issue.