In a previous post, we discussed bitcoin miners’ incentives to undertake a 51 percent attack given the current condition of the bitcoin market. We also speculated that high profits and free entry would cause more miners to enter the market, driving marginal mining profits to zero in the long run. Since then, the price of a bitcoin has declined over 40 percent and both the hash rate and the difficulty level of the bitcoin mining problem, which adjusts automatically to changes in the hash rate, appear to have leveled off. Our most recent calculations suggest the long run may have arrived.