51% Attacks

Definition ∞ A 51% attack occurs when a single entity controls over half of a blockchain network’s mining or staking power. This control allows the malicious actor to manipulate transaction order, reverse confirmed transactions, and prevent new transactions from being verified. Such an event undermines the integrity and security assurances of a decentralized ledger system. The ability to double-spend previously sent cryptocurrency is a primary objective of such an attack.
Context ∞ News reports often discuss the theoretical or actual occurrence of 51% attacks, particularly for smaller cryptocurrencies with less distributed hashing power. The vulnerability highlights a critical security concern for proof-of-work and proof-of-stake networks, influencing investor confidence and protocol development. Continuous monitoring of network decentralization remains a key factor in assessing the security posture of various digital assets.