I see a lot of people who don't know what the hell they're talking about.
If by "secret keys", you are referring to private keys, then there is no need to "hack" them. Here, go to this site --
http://directory.io . You can get every single private key in existence from that site. It doesn't matter though, since the digits amounting to the number of pages are more than all your fingers and toes combined. You can try to run a bot which checks every single private key you find there and your computer will die even before you get through 0.00000000000000001% of that "list". Now, if you're talking about hacking someone's computer in order to get their private keys, well, anyone can do that right now, so that's not really a theoretical scenario. Safeguard your computer and your files like a rational person would.
As for the people talking about "hacking" the blockchain, what exactly are you going on about? Do you even know what the blockchain is?