Your question is pretty unspecified. Bitcoin can be held by third parties.. but you shouln't let anybody hold your bitcoins.
These "hacks" don't happen because of btc being broken or those people being to stupid for anything.
There are flaws in their web application which led the attackers to gain control over the private keys.
I could imagine thats the mistake of the devs. Usually audits are reliable and i think exchanges should invest more into security than they currently do.
So the only way to prevent such hacks would be to build more secured software. But you will never gain 100% security.
Discussed bitcoin security issues will never be finished. While Bitcoin can not only be controlled by 1 party only, therefore we are given the option through (desktop, hardware, web, mobile wallet)
https://bitcoin.org/en/choose-your-wallet to make wallet and save btc, besides there are also some exchanges that offer similar services.
All of them certainly have their own security team, so it will be difficult
looking for common ground.
All wallet storage certainly has the risk of hack security, so making a backup of .dat wallet or storing private key in place is the most secure solution at the moment, although there are few instances where the backup file is corrupt so it can not be accessed again