You can't attack Bitcoin by just using computing power. Any attack will come from bankers accumulating most of the available coins, and using them for their own inter-company transfers. This will make some of us rich, but inhibit the use of Bitcoin as a general currency imho.
That's right, since Bitcoin is not an institution that can easily be hacked. It is a currency and whoever do an attack to it should start from banks or the whales to control it's momentum.