Off-chain infrastructure is the set of servers, APIs, bots, relays, and automation that operate outside a blockchain but still support protocol functions. In DeFi, these systems often collect market data, sign updates, route transactions, or trigger execution. They matter because a smart contract can be secure and still be harmed by bad off-chain inputs.
If an attacker compromises this layer, they may alter prices, abuse signing keys, or push fraudulent actions into an otherwise correct on-chain system. That can lead to faulty trades, drained vaults, or broken settlement logic without ever breaking the chain itself. Defenders reduce this risk by isolating keys, validating feeds, limiting privileges, monitoring anomalies, and designing redundancy so one compromised service cannot control the protocol.