owning 50% + eplison of the hash rate gives you the expectation of being able to undo an unlimited amount of history in theory. In practice you'd need to show

owning 50% + eplison of the hash rate gives you the expectation of being able to undo an unlimited amount of history in theory. In practice you'd need to show the world the blocks before they got to old or they'd be dropped due to an old timestamp. Buying up the ASICs would be the real cost, It seems like the chain is largely safe because of that. If the price drops enough that lots of mines liquidate it'd be good to keep an eye on where they go. If 50% of the hash power is dark large txs should rely on a whole lot of confirmations if at all.