there has been lots of attempts to hack bitcoin, break the cryptography, find the private keys to an address (which is impossible), ... and lots of other types of attempts but all have failed. and will continue to fail because the cryptography that is used by bitcoin is unhackable.

don't listen to the idiots such as @freightjoe who are spreading FUD.

there has been lots of hacks of web wallets, online wallets with no security measures, exchanges and things like that. but none of these are "hacking bitcoin" itself.