51 Percent Attack Vulnerability

51 Percent Attack Vulnerability describes the susceptibility of a Proof of Work blockchain to being controlled by a single entity or colluding group that commands the majority of the network hashrate. If an attacker gains this level of power, they can reorganize the chain, double-spend coins, or prevent new transactions from being confirmed.

This is a critical risk factor in systems design, particularly for smaller or less secure networks. The threat is mitigated by the decentralization of mining power and the economic cost of acquiring such massive amounts of hardware.

It represents the ultimate failure state for a decentralized ledger. Regulatory and security frameworks focus heavily on preventing this outcome.