Is it totally hack proof?
The blockchain tech has yet to be corrupted mostly due to the error-checking nature of the distributed ledger.
There have been many instances of bitcoin EXCHANGES that used unsafe software that have been successfully attacked. Most avoid the exchanges.
It has had more hackers trying to hack it than any other tech. But no, there are lot of threats to its existence. Ordinary computers in a few decades. Quantum could happen much sooner. The only protection is hashing of the public key. But there are many public keys on the block chain that still have value in the private keys.
The hackers will calculate the private key and spend the proceeds. There are other threats too, but that's the simplest threat.