51% attacks are a cryptocurrency’s worst nightmare. These attacks destroy confidence in a project and emphasize the need for carefully designed proof-of-work consensus. Below is a list of the five most prolific 51% attacks in crypto.
A 51% attack can occur when an attacker gains control of more than 50% of a network’s hashrate (the total mining power used to validate transactions on the network). Once an attacker has 50% or more of the hashrate on a network, they can invalidate transactions and even double-spend coins—invalidating the immutability and trustworthiness of a blockchain.