A 51% attack is a type of attack on a blockchain network in which a malicious actor or group of actors gains control of more than 50% of the network's mining power. This gives them the ability to control the network and perform malicious actions, such as:
Double-spending: This is when an attacker spends the same cryptocurrency twice. This is possible because the attacker can rewrite the blockchain to reflect a different transaction history.
Preventing transactions from being confirmed: The attacker can prevent new transactions from being confirmed, effectively halting the network.
Changing the order of transactions: The attacker can change the order of transactions in the blockchain, which could have implications for things like smart contracts.
How likely is a 51% attack?
The likelihood of a 51% attack depends on the size and security of the blockchain network. For example, it would be very difficult to launch a successful 51% attack on #bitcoin because the network is so large and secure. However, smaller blockchain networks are more vulnerable to 51% attacks.
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How can 51% attacks be prevented?
There are a number of ways to prevent 51% attacks, including:
Increasing the network hashrate: This makes it more difficult for an attacker to gain control of the network.
Decentralizing the network: This makes it more difficult for an attacker to control a majority of the network's mining power.
Using a different consensus mechanism: Some consensus mechanisms, such as proof-of-stake, are less vulnerable to 51% attacks than proof-of-work.
Examples of 51% attacks
There have been a number of 51% attacks on blockchain networks in the past. Some notable examples include:
Bitcoin Gold (BTG): In 2018, BTG was the victim of a 51% attack that resulted in the double-spending of $18 million worth of BTG.
Ethereum Classic (ETC): In 2019, ETC was the victim of a 51% attack that resulted in the double-spending of $5.6 million worth of ETC.
Verge (XVG): In 2017, XVG was the victim of a 51% attack that resulted in the double-spending of $100,000 worth of XVG.
Conclusion
51% attacks are a serious threat to #blockchain networks. However, there are a number of steps that can be taken to prevent these attacks. By increasing the #network hashrate, decentralizing the network, and using a different consensus mechanism, blockchain networks can make themselves more resistant to 51% attacks.