51% Attacks

A 51% attack occurs when a single entity or group gains control of more than half of a blockchain network's hashing power or mining capability. By controlling the majority of the network, the attacker can manipulate the blockchain ledger by preventing new transactions from gaining confirmations or reversing transactions that were already completed.

This capability allows the attacker to engage in double-spending, where they spend the same digital currency more than once. Such an attack undermines the trust and security of the entire decentralized system.

While highly costly and difficult to execute on established networks like Bitcoin, it remains a critical vulnerability for smaller proof-of-work blockchains. The attack essentially compromises the integrity of the consensus mechanism, rendering the ledger unreliable for users and exchanges.

It is a fundamental risk in the design of decentralized financial protocols. Understanding this threat is essential for evaluating the security posture of any digital asset.