Of all the responses so far, this I found most explanatory and its also boost my confidence in bitcoin in which I am sure if the current cappacity of the available computer can hack bitcoin, I am sure they would have attempted that. For the future, in which we all dont know yet, I am also optimistic that as at that time, its either there is an upgrade to the security apparatus of bitcoin or a mass adoption that any attempt to shut it down might disrupt the world order.