What Is a 51% Attack?A 51% attack refers to an attack on a blockchain—such as Bitcoin, for which such an attack is still hypothetical—by a group of miners controlling more than 50% of the network's mining hash rate or computing power. The attackers would be able to prevent new transactions from gaining confirmations, allowing them to halt payments between some or all users. They would also be able to reverse transactions that were completed while they were in control of the network, mean...