Sybil attack in crypto

A Sybil attack is when one actor creates many fake identities or nodes to gain undue influence over a peer-to-peer blockchain network. The attacker uses these fake nodes to skew votes, censor transactions, trace users, or cause conflicting history in the ledger. Such attacks can lead to double spending, broken finality, leaked privacy data, and a collapse of trust among users. Finality means a transaction is permanent and cannot be changed after confirmation. If Sybil attackers control a majority of influence they can reorder or erase transactions and break that finality. The name Sybil comes from an old story about a person with many identities and the term was later adopted by computer researchers to describe this kind of threat. In practice a Sybil actor spins up many nodes or accounts and then tries to be treated as many independent participants. The goal can be to win votes, become a chosen validator, or simply observe and trace user activity. A common worst case is when attackers amass enough computing or staking power to mount a majority attack and rewrite recent history. Blockchains use several defenses to make Sybil attacks costly or detectable. Proof-of-work forces attackers to invest real computation. Proof-of-stake forces attackers to lock value that can be penalized. Delegated systems limit decision power to a chosen set of representatives and tie incentives to reputation. Proof-of-personhood and identity proofs try to bind nodes to unique humans. Reputation systems and behavioral analytics flag outlier nodes and reduce their influence. Social graphs and peer ranking help detect clusters of related identities. Good network design limits how new nodes gain weight and spreads responsibilities across many independent operators. Operators and users can also practice caution by monitoring network health and using privacy-preserving tools. Despite the risks the community has learned from past incidents and adapted tools and best practices. The threat is real and can feel like a distant storm on the horizon. Yet there is tenderness in the response of builders who harden systems to protect small users. With layered defenses and vigilant stewardship decentralized systems can stay resilient and keep the promise of trusted, user-controlled digital value.