Blockchain is a distributed ledger that records transactions across many computers instead of one central database. Each block of data is linked to the previous one, and the network uses consensus rules to agree on what is valid. This design makes past records difficult to alter silently, which is why blockchain is often described as tamper-resistant rather than fully immutable.
In cyber security, blockchain matters because trust is built into the protocol layer. Defenders use it to verify asset transfers, audit records, and support systems where shared integrity is important. Attackers, however, target the surrounding ecosystem: stolen private keys, phishing, wallet-draining malware, malicious smart contracts, and compromised exchanges can all bypass the ledger’s protections. In practice, blockchain secures the record, but not always the endpoints, identities, or applications that interact with it.