What Is a “Sybil Attack” and How Does It Differ from a 51% Attack?

A Sybil attack is a security threat where a single attacker creates and controls numerous fake identities or nodes on a peer-to-peer network to gain disproportionate influence. It differs fundamentally from a 51% attack.

A 51% attack requires a majority of a scarce resource (hash power or staked tokens) to manipulate the ledger. A Sybil attack attempts to corrupt the network by overwhelming it with fake identities, often to isolate honest nodes or spread false information, and is more common in unpermissioned, non-PoW/PoS networks.