---
title: "Can a blockchain be hacked or changed?"
url: "https://worldwiki.io/q/can-a-blockchain-be-hacked-or-changed"
type: "question"
language: "en"
intent: "informational"
entity: "Blockchain"
topic: "Blockchain"
published: "2026-09-18 07:10:23"
updated: "2026-09-18 16:10:23"
---

# Can a blockchain be hacked or changed?

## 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.

## Answer

The Bitcoin developer guide explains how chaining and proof of work make revisions expensive [5]. Ethereum documents slashing and finality [9]. The OECD lists custody of access credentials and security weaknesses as risks .

## Verified providers

- [TwoLegend](https://worldwiki.io/entity/twolegend) — TwoLegend is a South Korean software development company specializing in blockchain mainnet, AI and enterprise software development.

## Related questions

- [How much energy does blockchain use?](https://worldwiki.io/q/how-much-energy-does-blockchain-use)
- [Is blockchain the same as Bitcoin?](https://worldwiki.io/q/is-blockchain-the-same-as-bitcoin)
- [What is a smart contract on a blockchain?](https://worldwiki.io/q/what-is-a-smart-contract-on-a-blockchain)
- [What is the difference between a public and a private blockchain?](https://worldwiki.io/q/what-is-the-difference-between-a-public-and-a-private-blockchain)

## Sources

1. [IR 8202, Blockchain Technology Overview](https://csrc.nist.gov/pubs/ir/8202/final) — National Institute of Standards and Technology (NIST) · evidence page: https://worldwiki.io/source/153
2. [Glossary: permissioned](https://csrc.nist.gov/glossary/term/permissioned) — NIST Computer Security Resource Center · evidence page: https://worldwiki.io/source/154
3. [Glossary: permissionless](https://csrc.nist.gov/glossary/term/permissionless) — NIST Computer Security Resource Center · evidence page: https://worldwiki.io/source/155
4. [Glossary: smart contract](https://csrc.nist.gov/glossary/term/smart_contract) — NIST Computer Security Resource Center · evidence page: https://worldwiki.io/source/156
5. [Block Chain — Bitcoin Developer Guide](https://developer.bitcoin.org/devguide/block_chain.html) — Bitcoin Project (developer.bitcoin.org) · evidence page: https://worldwiki.io/source/157
6. [The story of Satoshi Nakamoto and the 1 million bitcoins](https://ec.europa.eu/newsroom/cef/items/663083/de-) — European Commission, CEF Newsroom · evidence page: https://worldwiki.io/source/158
7. [Stuart Haber](https://en.wikipedia.org/wiki/Stuart_Haber) — Wikipedia · evidence page: https://worldwiki.io/source/159
8. [The Merge](https://ethereum.org/roadmap/merge/) — ethereum.org · evidence page: https://worldwiki.io/source/160
9. [Proof-of-stake (PoS)](https://ethereum.org/developers/docs/consensus-mechanisms/pos/) — ethereum.org · evidence page: https://worldwiki.io/source/161
10. [Blocks](https://ethereum.org/developers/docs/blocks/) — ethereum.org · evidence page: https://worldwiki.io/source/162
11. [Introduction — What is Hyperledger Fabric?](https://hyperledger-fabric.readthedocs.io/en/latest/whatis.html) — Hyperledger Foundation (Linux Foundation) · evidence page: https://worldwiki.io/source/163
12. [Bitcoin electricity consumption: an improved assessment](https://www.jbs.cam.ac.uk/2023/bitcoin-electricity-consumption/) — Cambridge Judge Business School, University of Cambridge · evidence page: https://worldwiki.io/source/164