Okuzeka
Blockchain & Crypto vocabulary · Regulation, Security & Risk

51% attack

Meaning in blockchain & crypto, with examples

nounAdvanced term

In blockchain & crypto, 51% attack means: An attack in which one person or group controls more than half of a network's mining power or stake, which lets them reverse their own recent transactions and spend the same coins twice.

In Turkish: %51 saldırısı, çoğunluk saldırısı

How it is used

Read as 'fifty-one percent attack'. Used in security discussions, especially about smaller proof-of-work coins where renting enough hash rate is cheap. It is closely linked to double spending. Exchanges respond by raising the number of confirmations they require.

Example sentences

  1. After the 51% attack, the exchange raised the required confirmations from 12 to 500.

  2. A 51% attack cannot take coins from other people's wallets, but it can reverse the attacker's own payments.

Common collocations

  • suffer a 51% attack
  • launch a 51% attack
  • 51% attack risk
  • double spending
  • hash rateThe total computing power that miners use to secure a proof-of-work network, measured in hashes per second. A higher hash rate makes the network harder to attack.
  • proof of workA consensus mechanism in which miners use computing power to solve a puzzle before they can add a block. It makes attacks very expensive but uses a lot of energy. Bitcoin uses it.
  • confirmationProof that a transaction has been included in a block. Each new block added after it counts as one more confirmation, and more confirmations make the transaction harder to reverse.
  • consensus mechanismThe set of rules that lets the computers in a blockchain agree on which transactions are valid and in what order, without trusting a central authority. Proof of work and proof of stake are the best-known types.
  • exploitAn attack that takes advantage of a bug or design weakness, often in a smart contract or bridge, to steal funds or make a system behave in a way its creators did not intend.

More terms: Regulation, Security & Risk

Practise with graded reading

Reading at the right level is the fastest way to make new words stick. Pick free English books by level: