51% Attack

51% Attack is defined as a situation where more than half of the computer power running a blockchain are controlled by one person or one group of people with evil intentions. That person or group with the majority power can manipulate transactions in their favor.

In a 51% attack, the attackers might be able to:

  • Prevent new transactions from being included in the blockchain.
  • Reverse transactions so they could spend the same money again and again, known as a double-spend.

There are theories that it may even take less than the majority computing power (51%) to manipulate a cryptocurrency.