51 Percent Attack - Blockchain
Description
Via Molly White:
51% attack or majority attack:
"an attack on a blockchain made possible when a single person or group gains control of over 50% of a blockchain’s hashing power, enabling them to block new transactions from being confirmed as well as change the ordering of new transactions. It also allows the malicious agents to essentially rewrite parts of the blockchain and reverse their own transactions, leading to an issue known as double spending. (CoinDesk)"