What is a 51% Attack?

What is a 51% Attack

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A 51% attack is an attack on a blockchain in which an attacker can control more than 50% of the network’s mining hash rate or computing power. This allows the attacker to have most of the network’s mining power, allowing them to double-spend coins, prevent new transactions from being confirmed, and halt the entire network.

The attack occurs when the attacker can control over half of the blockchain’s mining power. With this majority, the attacker can choose which transactions to validate and which to ignore. This means that they can reverse transactions that they have made, allowing them to double-spend coins. The attacker can also prevent new transactions from being added to the blockchain, halting the entire network.

The probability of a 51% attack occurring increases as the mining power becomes more centralized, as a small number of miners would have a larger percentage of the total mining power. This is why decentralization is an important aspect of blockchain technology, as it helps to prevent a single entity from gaining too much control over the network.

Popular 51% Attacks

Some examples of 51% attacks that have occurred on various blockchains include:

  • Ethereum Classic (2019): In January 2019, Ethereum Classic (ETC) suffered a 51% attack in which the attacker could double-spend around $1.1 million worth of ETC.
  • Bitcoin Gold (2018): In May 2018, the Bitcoin Gold (BTG) network suffered a 51% attack in which the attacker could double-spend around $18 million worth of BTG.
  • ZenCash (2018): In June 2018, the ZenCash (ZEN) network suffered a 51% attack in which the attacker could double-spend around $550,000 worth of ZEN.
  • Verge (2018): In April 2018, the Verge (XVG) network suffered a 51% attack in which the attacker could double-spend around $1.7 million worth of XVG.
  • Electroneum (2018): In December 2018, the Electroneum (ETN) network suffered a 51% attack in which the attacker could double-spend around $1.1 million worth of ETN.
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These are just a few examples of 51% attacks on various blockchains. Of course, blockchains with larger mining pools and more decentralized mining power are less vulnerable to 51% attacks.

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