> They've go this 51% vulnerability that is well known and hypothetically cannot be truly closed. Instead, we rely on the idea that mounting such an attack would be "too expensive". But at the same time, the cost/benefit of mounting such an attack is fairly easy to estimate using public data - all you really need to know is the cost to get to 51% and stay there for a given amount of time, which you can infer by monitoring mining activity, and the current price of the currency you'd want to attack. And you have to assume that whenever the cost of mounting such an attack dips below the benefit, such a thing _will_ happen.

Or, to turn this around, if X is the amount of money needed to sustain a 51% attack for 1 block, then you have to wait for 1 confirmation for every X amount of coins received.