indeed to a security problem if we know and understand the technology surely will say that in general the bitcoin is very secure. Because it has a very system bitcoin complex and well enough to avoid the presence of hacking. But one thing can indeed give the worst thing for us is that when we can't control or securing the secret key from the wallet it is certain we will lose all of the funds.
BITCOIN has been hacked 1,000's of times, and people have lots 10's of millions of USD
There is so much ignorance here, I think not 1 in 1,000 on this board understands anything about BTC.
Say the 51% quote above, it has NOTHING to do with hashrate, it has to do with nodes, and that +51% of the nodes must accept the longest chain for a transaction to be confirmed, nothing to do with the subject at hand. Sure if someone controlled +51% of the nodes then they could create their own transactions and that would seriously screw the block-chain, but the problem is that ain't going to happen cuz only one chinese miner controls 51% of the nodes, and he aint' going piss in his own soup bowl.
Ten's of thousands of software people world-over are working to crack the private-keys, and targeted cracking already exists the problem is cracking high-value accounts.
The average BTC account if valid is 0.05 BTC, and its what 2% of the space, Randomly creating Private-keys and looking for money doesn't work, so then one must focus on addresses with money and try to 'guess/calculate' the private-key for that address, that is where the real hacking is going on.
The majority of people on this board, would give their BTC to an exchange for a 'free shit coin' this is how most BTC is lost, not by hacking, but by idiots trying to get free shit-coins (FORKS).