What is 51% Attack?

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51% attack is the situation where the majority of a blockchain network’s computing power is taken over. When this attack occurs, the attacker can alter block production and transaction validations for their own benefit. The transparent structure of the network is disrupted, and user trust is undermined. Therefore, a 51% attack is considered one of the most serious threats to cryptocurrency networks and is critically important for the sustainability of decentralization.

What is 51% Attack?

51% attack means that more than half of the computing power of a blockchain network is controlled by a single person or group. This control allows the attacker to manipulate transactions, rearrange blocks at will, and disrupt the normal operation of the network. Smaller-scale networks are especially more vulnerable to such attacks because they have fewer miners.

Double Spending

Double spending is the possibility of using the same cryptocurrency more than once. In a 51% attack, the attacker can first confirm a transaction and then create an alternative version of the chain to invalidate it. This way, the same asset is spent twice. This creates a major security vulnerability, particularly in commercial payments, and can lead to significant losses for merchants.

Transaction Blocking

Transaction blocking is one of the key consequences of a 51% attack. The attacker can prevent or completely reject transactions they do not wish to validate on the network. This creates serious congestion on the blockchain, and transactions may remain unconfirmed for long periods or never be processed. Transaction blocking leads to a loss of user trust and undermines the reliability of digital payment systems.

Digital Currency Risk

Digital currency risk refers to the economic impact of a 51% attack. When such an attack occurs, the network’s security is questioned, and user confidence in the associated cryptocurrency decreases. This loss of confidence can directly result in price declines. In smaller-scale projects, token values can drop rapidly following an attack, causing investors to suffer major losses. For this reason, a 51% attack is not only a technical threat but also a serious risk factor that affects market value.

How Does 51% Attack Work?

51% attack works when the party that gains control of the majority of a blockchain network’s computing power directs the system for its own benefit. The attacker achieves dominance in block production and decides which transactions will be confirmed. This allows them to perform double spending, block transactions, or manipulate the network by creating an alternative chain. In networks with low hash power, the likelihood of such an attack is higher, as it is easier for the attacker to gain the necessary computing power.

How to Prevent 51% Attack?

The most effective way to prevent a 51% attack is to increase the number of miners or validators in the network and distribute computing power. The more participants there are, the harder it becomes for an attacker to seize the majority. In addition, strong consensus mechanisms, regular security audits, and on-chain monitoring systems help reduce the risk. In large networks, high computing power makes the cost of an attack astronomically high, deterring potential attackers.

Examples of 51% Attacks

51% attacks have occurred many times in cryptocurrency history and caused serious security issues across different networks. Here are some notable examples:

Bitcoin Gold (2018): In May 2018, the Bitcoin Gold network was attacked, resulting in approximately $18 million in double spending.
Vertcoin (2018): In December 2018, the Vertcoin network was attacked multiple times, with attackers reorganizing the chain and rolling back over 100 blocks.
Ethereum Classic (2019): In January 2019, Ethereum Classic suffered a 51% attack, with about $1 million worth of double spending detected.
Ethereum Classic (2020): The same network was attacked several more times in August 2020, with over 7,000 blocks rewritten, deepening the trust issues.
Grin (2020): In November 2020, the privacy-focused Grin network was attacked; the majority of its hash rate was seized, and block production was manipulated.
Bitcoin SV (2021): In August 2021, Bitcoin SV was attacked, experiencing multiple reorganizations, which raised questions about the network’s reliability.

These attacks show that networks with lower hash power are more vulnerable. Compared to large-scale networks, small and medium-sized projects are more exposed to 51% attacks.

FAQ

What is the Purpose of a 51% Attack?

The purpose of a 51% attack is to take control of a blockchain network for personal gain and manipulate transactions. It is generally used to double spend, block transactions, or destabilize the network.

Can Bitcoin Face a 51% Attack?

Theoretically yes, but the computing power of the Bitcoin network is extremely high. Carrying out such an attack would require astronomical costs. In practice, the likelihood of Bitcoin facing this risk is very low.

Which Networks are More Vulnerable to a 51% Attack?

Smaller blockchain networks with low hash power and fewer miners are more vulnerable. In such networks, seizing majority control is easier and less costly.

How Can You Protect Against a 51% Attack?

A strong consensus mechanism, widespread miner participation, and high computing power help reduce the risk of a 51% attack. Regular network audits and updated security protocols are also effective protection methods.

2025-09-05

Legal Notice

The information, comments, and evaluations contained in this content do not constitute investment advice. This content is not intended to be prescriptive in any way and is intended to provide general information. It does not constitute investment advice. CoinTR cannot be held responsible for any transactions made based on this information or any losses that may arise.

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