To answer this question we need to understand what hacking a blockchain means. We all know that coins live on the blockchain and you can send/receive them by accessing them through your keys.
This creates the illusion that hacking the blockchain would mean that somebody would crack open the encryption and steal the coins. The fact is that as long as you can get your hands on the coins without the owners permission, it would be called hacking. No matter if you cracked the encryption or not.
The blockchain can theoretically be hacked in a number of ways, but most common hacking attacks include, Sybil attack, Routing attack, DDOS, etc. Their is one truth of hacking - theoretically, everything is hackable.
As you can see that blockchain hasn't put an end to hacking. In fact it has even inspired some new ways of disrupting the network or trying to control the consensus. Nevertheless, the blockchains are still some of the most secure locations to keep your money in. Protecting the keys and passwords is each individuals personal responsibility.