{"id":717,"slug":"can-a-blockchain-be-hacked-or-changed","question":"Can a blockchain be hacked or changed?","intent":"informational","language":"en","url":"https://worldwiki.io/q/can-a-blockchain-be-hacked-or-changed","entity":{"slug":"blockchain","name":"Blockchain","url":"https://worldwiki.io/entity/blockchain"},"answer":{"short_answer":"Changing past records is hard but not impossible. Each block contains the hash of the previous block, so editing an old transaction means rebuilding every block after it. On a proof-of-work chain, that would take control of most of the network's computing power, known as a 51% attack. On Ethereum's proof-of-stake chain, it would take at least half of the staked ETH, and attackers can lose that stake. Wallets, keys and smart contract code can also be attacked separately.","detailed_answer":"<p>The Bitcoin developer guide explains how chaining and proof of work make revisions expensive <span class=\"ref\">[5]</span>. Ethereum documents slashing and finality <span class=\"ref\">[9]</span>. The OECD lists custody of access credentials and security weaknesses as risks .</p>","format":"paragraph","confidence":75,"verified_at":"2026-09-18 07:10:23","updated_at":"2026-09-18 16:10:23"},"sources":[{"id":153,"title":"IR 8202, Blockchain Technology Overview","url":"https://csrc.nist.gov/pubs/ir/8202/final","publisher":"National Institute of Standards and Technology (NIST)","type":"government","accessed_at":"2026-09-18 18:01:11"},{"id":154,"title":"Glossary: permissioned","url":"https://csrc.nist.gov/glossary/term/permissioned","publisher":"NIST Computer Security Resource Center","type":"government","accessed_at":"2026-09-18 18:01:11"},{"id":155,"title":"Glossary: permissionless","url":"https://csrc.nist.gov/glossary/term/permissionless","publisher":"NIST Computer Security Resource Center","type":"government","accessed_at":"2026-09-18 18:01:12"},{"id":156,"title":"Glossary: smart contract","url":"https://csrc.nist.gov/glossary/term/smart_contract","publisher":"NIST Computer Security Resource Center","type":"government","accessed_at":"2026-09-18 18:01:13"},{"id":157,"title":"Block Chain — Bitcoin Developer Guide","url":"https://developer.bitcoin.org/devguide/block_chain.html","publisher":"Bitcoin Project (developer.bitcoin.org)","type":"official","accessed_at":"2026-09-18 18:01:13"},{"id":158,"title":"The story of Satoshi Nakamoto and the 1 million bitcoins","url":"https://ec.europa.eu/newsroom/cef/items/663083/de-","publisher":"European Commission, CEF Newsroom","type":"government","accessed_at":"2026-09-18 18:01:17"},{"id":159,"title":"Stuart Haber","url":"https://en.wikipedia.org/wiki/Stuart_Haber","publisher":"Wikipedia","type":"other","accessed_at":"2026-09-18 18:01:17"},{"id":160,"title":"The Merge","url":"https://ethereum.org/roadmap/merge/","publisher":"ethereum.org","type":"official","accessed_at":"2026-09-18 18:01:18"},{"id":161,"title":"Proof-of-stake (PoS)","url":"https://ethereum.org/developers/docs/consensus-mechanisms/pos/","publisher":"ethereum.org","type":"official","accessed_at":"2026-09-18 18:01:20"},{"id":162,"title":"Blocks","url":"https://ethereum.org/developers/docs/blocks/","publisher":"ethereum.org","type":"official","accessed_at":"2026-09-18 18:01:21"},{"id":163,"title":"Introduction — What is Hyperledger Fabric?","url":"https://hyperledger-fabric.readthedocs.io/en/latest/whatis.html","publisher":"Hyperledger Foundation (Linux Foundation)","type":"official","accessed_at":"2026-09-18 18:01:21"},{"id":164,"title":"Bitcoin electricity consumption: an improved assessment","url":"https://www.jbs.cam.ac.uk/2023/bitcoin-electricity-consumption/","publisher":"Cambridge Judge Business School, University of Cambridge","type":"academic","accessed_at":"2026-09-18 18:01:23"}],"published_at":"2026-09-18 07:10:23"}