{"id":"51percent-attack","title":"51% Attack","content":"A **51% attack** occurs when a [blockchain](https://iq.wiki/wiki/blockchain) is targeted by a coalition of miners who possess more than 50% of the total [mining ](https://iq.wiki/wiki/mining)hash rate on the network. If this group gains ownership of 51% of the network's nodes, it theoretically grants them the authority to modify the [blockchain](https://iq.wiki/wiki/blockchain).[\\[1\\]](#cite-id-wltt2pcif1m)\\\n$$widget0 [YOUTUBE@VID](01a7HAkEK3I)$$\n\n# Overview\n\nA [blockchain](https://iq.wiki/wiki/blockchain) achieves decentralization by ensuring that no single individual or specific group holds control over the network. This decentralized structure is crucial because all participants within the blockchain ecosystem must reach a consensus on the present state of the blockchain. This requirement for unanimous agreement among the widely distributed network participants establishes a high level of certainty regarding the authenticity of the block's state.[\\[2\\]](#cite-id-48l4ylloarn)\n\nA 51% attack refers to a deliberate attack on a blockchain in which a group gains control over more than 50% of the network's hashing power, which is the computational capability used to solve cryptographic puzzles. This group subsequently introduces a modified version of the blockchain into the network at a precise juncture. Theoretically, the network might accept this altered blockchain due to the attackers' majority control over the network.[\\[1\\]](#cite-id-wltt2pcif1m)[\\[2\\]](#cite-id-48l4ylloarn)[\\[3\\]](#cite-id-45gt55lheed)\n\n# Impacts of 51% Attack\n\n## Reduced Miner Rewards\n\nIn a 51% attack, a transaction might be reversed even before it is verified. This results in [double spending](https://iq.wiki/wiki/double-spending-problem). As the attackers take their shares, legitimate miners also make less money updating the network.[\\[4\\]](#cite-id-brvnnevnzr5)[\\[2\\]](#cite-id-48l4ylloarn) A 51% assault on a blockchain could adversely impact a [cryptocurrency](https://iq.wiki/wiki/cryptocurrency)'s reputation, which would cause investors to sell their crypto, depreciating its value.[\\[5\\]](#cite-id-gxk09x4yuy)[\\[6\\]](#cite-id-xqcmssv2ur8)\n\n## Network Disruption\n\nAs long as a blockchain employs a [Proof-of-Work (PoW)](https://iq.wiki/wiki/proof-of-work-pow) mechanism to validate transactions, perpetrators can intentionally disrupt the network by impeding the confirmation and sequential arrangement of blocks.[\\[4\\]](#cite-id-brvnnevnzr5) A 51% assault has a significant negative effect on the miner's computational capabilities. As a result, it takes longer for the transaction to be approved and recorded in a [block](https://iq.wiki/wiki/block). As a result, the [blockchain](https://iq.wiki/wiki/blockchain) network becomes compromised, enabling the attackers to execute transactions faster than the miner.[\\[4\\]](#cite-id-brvnnevnzr5)\n\n# 51% Attack Prevention\n\nBlockchains employ several strategies to prevent 51% attacks. One of such strategies is to incentivize a greater number of participants to join the network and operate their own nodes, thereby bolstering a strong network community. A higher number of participants contributing resources makes it more challenging for a sole entity to exert dominance over the network.[\\[3\\]](#cite-id-45gt55lheed)[\\[4\\]](#cite-id-brvnnevnzr5)\n\nIn a small blockchain network, a single miner could potentially dominate as the majority participant. Blockchain networks employing the [Proof of Work](https://iq.wiki/wiki/proof-of-work-pow) (PoW) consensus mechanism typically implement a requirement that miners regularly update their equipment. Neglecting this can result in them forfeiting block rewards and falling behind other miners within the network. [\\[4\\]](#cite-id-brvnnevnzr5)\n\nTo mitigate the risk of a 51% attack, blockchain networks can opt for the [Proof of Stake (PoS)](https://iq.wiki/wiki/proof-of-stake) consensus mechanism, which is generally considered a more secure alternative to [Proof of Work](https://iq.wiki/wiki/proof-of-work-pow) (PoW) because it is more challenging for an attacker to acquire the larger majority of the staked cryptocurrency compared to most of the mining power in a [PoW](https://iq.wiki/wiki/proof-of-work-pow) [blockchain](https://iq.wiki/wiki/blockchain).[\\[4\\]](#cite-id-brvnnevnzr5)[\\[5\\]](#cite-id-gxk09x4yuy)[\\[8\\]](#cite-id-apado95xybl)\\\n![1671478532822.jpeg](https://ipfs.everipedia.org/ipfs/Qmd5wWFUVcUL1p6kVD5tUbUzihjdmnnpfPJh8qUdh4SugC)\n\n## Past Examples of 51% Attacks\n\nThe majority of 51% attacks are directed towards smaller cryptocurrencies. Experts suggest that major cryptocurrencies are unlikely to fall victim to a successful 51% attack due to the substantial cost associated with gaining control of over half of the mining power. The following are blockchain networks that have experienced a 51% attack in the past:\n\n* In 2018, an attack on [Bitcoin Gold](https://iq.wiki/wiki/bitcoin-gold) (BTG) led to the [double spending](https://iq.wiki/wiki/double-spending-problem) of over $18 million worth of the currency. In 2020, BTG encountered another 51% attack. Within a span of two days, the [blockchain](https://iq.wiki/wiki/blockchain) underwent two reorganizations, enabling double-spending activities that resulted in substantial financial losses. However, this attack was quickly stopped to prevent further loss. [\\[4\\]](#cite-id-brvnnevnzr5)[\\[6\\]](#cite-id-xqcmssv2ur8)\n* [Ethereum Classic](https://iq.wiki/wiki/ethereum-classic) (ETC), a cryptocurrency that emerged from a hard fork of [Ethereum](https://iq.wiki/wiki/ethereum) in 2016, fell victim to a 51% attack in 2020. This incident resulted in the reported theft of several million dollars.[\\[6\\]](#cite-id-xqcmssv2ur8)\n* [Bitcoin SV](https://iq.wiki/wiki/bitcoin-sv) (BSV) faced three attacks in 2021. These attacks enabled hackers to manipulate or erase the most recent blocks by gaining control over the network.[\\[6\\]](#cite-id-xqcmssv2ur8)","summary":"A 51% attack is a potential threat to blockchains, where a group controls over 50% of network hash power, theoretically allowing blockchain modification.","images":[{"id":"QmWPqMZVZmCgpMqtdxJjSw2epZRVv782bGmMPrmrFknu7B","type":"image/jpeg, image/png"}],"categories":[{"id":"glossary","title":"glossary"}],"tags":[],"media":[{"id":"QmSnhnucHWn86Jg1f268q7dNUtvUoa9it412mEJ6hWZp1D","size":"0.03","name":"How_dangerous_is_51_percent_attack.webp","type":"GALLERY","source":"IPFS_IMG"},{"id":"QmTPVXG6mgpAxqu34xsNZPSjmcz8P9igNQqM6QeELey6XP","size":"0.01","name":"download (1).jpeg","type":"GALLERY","source":"IPFS_IMG"},{"id":"https://www.youtube.com/watch?v=01a7HAkEK3I","size":"0","name":"01a7HAkEK3I","type":null,"source":"YOUTUBE"},{"id":"Qmd5wWFUVcUL1p6kVD5tUbUzihjdmnnpfPJh8qUdh4SugC","size":"0.16","name":"1671478532822.jpeg","type":"GALLERY","source":"IPFS_IMG"}],"metadata":[{"id":"references","value":"[{\"id\":\"wltt2pcif1m\",\"url\":\"https://www.investopedia.com/terms/1/51-attack.asp\",\"description\":\"51% Attack: Definition, Who Is At Risk, Example, and Cost\",\"timestamp\":1691683278007},{\"id\":\"48l4ylloarn\",\"url\":\"https://www.coindesk.com/learn/what-is-a-51-attack/\",\"description\":\"What Is a 51% Attack?\",\"timestamp\":1691683685403},{\"id\":\"45gt55lheed\",\"url\":\"https://academy.binance.com/en/glossary/51-percent-attack\",\"description\":\"What Is a 51% Attack?\",\"timestamp\":1691685977130},{\"id\":\"brvnnevnzr5\",\"url\":\"https://www.section.io/engineering-education/understanding-the-51-attack-on-blockchain/\",\"description\":\"Understanding a 51% Attack on the Blockchain\",\"timestamp\":1691687979033},{\"id\":\"gxk09x4yuy\",\"url\":\"https://www.sofi.com/learn/content/51-attack/\",\"description\":\"What Is a 51% Attack?\",\"timestamp\":1691689117191},{\"id\":\"xqcmssv2ur8\",\"url\":\"https://www.fool.com/terms/0-9/51-percent-attack/\",\"description\":\"What Is a 51% Attack?\",\"timestamp\":1691727285823},{\"id\":\"m4x9ustkx3\",\"url\":\"https://cointelegraph.com/news/what-is-a-51-attack-and-how-to-detect-it\",\"description\":\"What is a 51% attack and how to detect it?\",\"timestamp\":1691727546467},{\"id\":\"apado95xybl\",\"url\":\"https://originstamp.com/blog/what-is-a-51-attack-on-the-blockchain/#:~:text=Because%20it%20is%20more%20challenging,attack%20on%20a%20PoS%20blockchain.\",\"description\":\"originstamp.com - What is a 51% Attack on the Blockchain?\",\"timestamp\":1695172530339}]"},{"id":"previous_cid","value":"\"https://ipfs.everipedia.org/ipfs/QmSNaRGEZa1CKRMc3qvEr7reptepWfgpCe4QM8QogokREy\""},{"id":"commit-message","value":"\"Removed 51% attack overview\""},{"id":"previous_cid","value":"QmSNaRGEZa1CKRMc3qvEr7reptepWfgpCe4QM8QogokREy"}],"events":[],"user":{"id":"0x8af7a19a26d8fbc48defb35aefb15ec8c407f889"},"author":{"id":"0x8eBEb49FEFC02bd8C053F588F58A85e72E4cF9C9"},"operator":{"id":"0x1E23b34d3106F0C1c74D17f2Cd0F65cdb039b138"},"language":"en","version":1,"linkedWikis":{"blockchains":[],"founders":[],"speakers":[]},"recentActivity":"{\"items\":[{\"id\":\"0f145584-7f9f-4247-a332-7bce1a18098e\",\"title\":\"51% Attack\",\"description\":\"A 51% attack is a potential threat to blockchains, where a group controls over 50% of network hash power, theoretically allowing blockchain modification.\",\"timestamp\":\"2026-06-01T01:44:18.229Z\",\"category\":\"glossary\",\"status\":{\"icon\":\"RiGlobalLine\",\"label\":\"Wiki Updated\",\"iconClassName\":\"text-green-500\"},\"user\":{\"name\":\"0x8eBEb49FEFC02bd8C053F588F58A85e72E4cF9C9\",\"address\":\"0x1E23b34d3106F0C1c74D17f2Cd0F65cdb039b138\"},\"button\":{\"label\":\"View Summary\",\"icon\":\"RiFileTextLine\"},\"summarySections\":[{\"title\":\"Linked Wikis\",\"subtitle\":\"One linked wiki was removed and a different linked wiki was added.\",\"variant\":\"modified\",\"changeCount\":2,\"changes\":[\"Removed linked wiki with id \\\"defi\\\" and title \\\"Decentralized Finance\\\"\",\"Added linked wiki with id \\\"glossary\\\" and title \\\"glossary\\\"\"]},{\"title\":\"Tags\",\"subtitle\":\"Tag list was changed; the 'Glossary' tag was removed and the tags array is now empty.\",\"variant\":\"modified\",\"changeCount\":2,\"changes\":[\"Removed tag with id \\\"Glossary\\\"\",\"Tags array is now [] (no tags)\"]},{\"title\":\"Metadata\",\"subtitle\":\"A stored hash value was removed and new metadata metrics were added.\",\"variant\":\"modified\",\"changeCount\":5,\"changes\":[\"Removed metadata field \\\"hash\\\" with value \\\"Qmd5wWFUVcUL1p6kVD5tUbUzihjdmnnpfPJh8qUdh4SugC\\\"\",\"Added metadata \\\"words-changed\\\" = \\\"34\\\"\",\"Added metadata \\\"percent-changed\\\" = \\\"8.34\\\"\",\"Added metadata \\\"blocks-changed\\\" = \\\"content, tags, events\\\"\",\"Added metadata \\\"wiki-score\\\" = \\\"72\\\"\"]}]}]}"}