51% Attack
A 51% attack refers to a scenario where a group of miners, controlling over half of the network's mining hash rate, can potentially manipulate a cryptocurrency's blockchain. Having control over 51% of the network's nodes theoretically enables them to modify the blockchain's history.
Key Points
Cryptocurrency blockchains are decentralized databases that log each transaction. A 51% attack happens when miners command more than half of the network's mining power, allowing them to disrupt the recording of new blocks by stopping other miners from finalizing blocks. Modifying already confirmed blocks is challenging due to the interconnected information in blockchains like Bitcoin's. While significant cryptocurrencies like Bitcoin or Ethereum are less vulnerable, smaller blockchains could be easier targets for such attacks.
Comprehensive Understanding of a 51% Attack
A blockchain serves as a secure, encrypted ledger that chronicles transactions and details about them, achieving consensus on transactions through a verification process. Sealed blocks, interconnected through cryptographic methods that incorporate previous block data into each new block, ensure that altering confirmed blocks is nearly infeasible. During a 51% attack, a dominating group might try to impose an altered version of the blockchain at a critical juncture. However, changing previously confirmed transactions, especially those before a 'checkpoint' where transactions are permanently etched into Bitcoin's blockchain, remains highly challenging, if not impossible.