Not true, necessarily. There have been proposals to form a "web of trust" for miners, which would prevent this sort of thing from happening. Miners who have be

Not true, necessarily. There have been proposals to form a "web of trust" for miners, which would prevent this sort of thing from happening. Miners who have been on the network for longer would have greater authority than new miners, regardless of computational ability. If a 51% attack occurs, it would in effect fork the blockchain, because the WoT-enabled miners would not accept their signed blocks. You can fork the blockchain now if you want - it's just a matter of getting enough people to agree with you for those coins to have value. I'm not saying it would be _good_ for Bitcoin - but this is not an insurmountable problem from a tech standpoint.