ya the code for BC is rather un-breakable, but if you have bitcoins store them OFF LINE. much easier to hack a wallet/wallet host site than bitcoin itself. there was rumor of a 51% attack being possible a few days ago when a group of miners conglomerated and had like 46% of the total gigahash rate. "the network is free and open, so if someone were to have enough computational power (which would cost a huge amount by itself), there is no bitcoin authority to stop them from doing so."
so they could double spend coins, invalidate legit transactions and prevent miners from mining coins for a short time.
so they could double spend coins, invalidate legit transactions and prevent miners from mining coins for a short time.