A 51% attack is a type of cyberattack in the cryptocurrency industry, where an individual or group gains control of over 50% of the computational power of a blockchain network. These entities have control over most of the blockchain's mining power, allowing them to manipulate the network's transactions.

For example, since they have this control, cyberattackers can double-spend assets and manipulate transactions.

Blockchain networks implement consensus protocols, such as Proof of Work (PoW) or Proof of Stake (PoS), to prevent 51% attacks from happening. These consensus protocols distribute computational power across the blockchain network, making it harder for entities to control the majority of the network's power.