The protocol itself cannot be hacked. If a hacker infiltrates a single or even a group of bitcoin clients and changes the protocol on those computers, it would be seen by the network as a fork and not accepted by the rest of the network.
Wallets on the other hand, can be hacked, or at least brute forced "collisions" can happen. No need to get someone's passwords or physical wallet.dat. You can simply type in any acceptable combination of chars and gain access to any coins in the address (if any exist) that corresponds to that private key. Now, on that note, the likelihood of someone randomly guessing yours or anyone else's private key, is so astronomically low that it is virtually a non-issue. It would take a lot of time and computer resources to even find a private key that contains coins.
This is a good discussion on this.
https://steemit.com/bitcoin/@orionsbelt/how-many-bitcoin-addresses-are-thereLet's see, 9x1059 combinations, If I guess 100,000,000 combinations per sec ( = 108 combinations per sec) it would only take about 9x1051 seconds.
Hmmm... 60 sec per minute x 60 min per hr x 24 hr per day x 365 days per year = 31,536,000 seconds per year. ( = approx 3x107 sec/yr)
9x1051 seconds / (3x107 seconds per year) = 3x1044 years.
uh oh, I'll need to speed thing up a bit.
To try all combinations in 30 years, I need to check 9x1059 / (30 years x 3x107 sec/yr) = 1051 combinations per sec for 30 years.
Yikes!
edit, yes, if this became trivial to process, then Bitcoin ded. D. E. D. dead