51% Attack

An event where an attacker attempts to control over 50% of a proof of work blockchains mining hash rate or computing power, or in the case of a proof of stake blockchain, over 50% of all cryptocurrencies staked in the network's validator staking pool.

Controlling over 50% of a blockchain network can potentially enable an attacker to reverse a transaction, commit a double spend or manipulate the supply of the blockchains tokens.