Blockchains are protected by a combination of strong security features: cryptography, how records are linked together, decentralization, and agreement processes. Once information is added to a blockchain, it’s extremely difficult to change because of these linked records and the fact that copies are stored on many computers. However, even the most secure blockchain isn’t foolproof. Mistakes made by users, flaws in smart contracts, or unsafe key management can create vulnerabilities. Attacking a major blockchain is very expensive, requiring a huge investment, which discourages most attackers. To get the most out of blockchain security, it’s important to use well-established blockchains, carefully review smart contracts for errors, and protect your private keys.