A 51% attack is a type of attack that is seen as a potential threat to many blockchain networks running on blockchain technologies. By taking control of enough miners on a blockchain network, this type of attack can cause the network's transactions to be controlled, double-spending, or even a complete network crash.

A 51% attack means that attackers need to capture half or more of the network's hashing power in order to increase their control of the network and gain transaction processing power. To carry out this attack, attackers often use various methods, such as owning or leasing miners with high hashing power to join the network.

This attack is much more difficult to carry out on cryptocurrencies with high participation than on cryptocurrencies with low participation. As transactions go backwards, it becomes correspondingly harder for attackers to modify transactions.

What Can Attackers Do with a 51% Attack?

Attackers who have the majority of hash power can verify the transactions they want because they have the majority on the network. Attackers use this power for their own benefit. With a successful 51% attack, the consensus structure of the network is disabled, and attackers can spend the same cryptocurrency again by performing a reverse transaction.

What Is Required for an Attacker to Carry Out a 51% Attack?

For a 51% attack, attackers need to have captured that many nodes and have already prepared an alternative blockchain network that can be added at the right time. They will then need to block the main network.

What Is the Importance of a Cryptocurrency's Participation Ratio for a 51% Attack?

The higher the participation ratio of a cryptocurrency in the network, the more difficult it is for attackers to carry out a 51% attack. This is because the number of nodes and hashing power required for attackers to reach 51% increases.

Which Cryptocurrencies Are Vulnerable to a 51% Attack?

Altcoins are much more likely to be hit by a 51% attack than Bitcoin and similar cryptocurrencies with large volumes.

What to Expect from a 51% Attacked Cryptocurrency? What Is the Example?

One of the assets that suffered a 51% attack and suffered losses with double-spending is Bitcoin Gold. Bitcoin Gold (BTG) was subjected to a 51% attack on January 27, 2020, and Bitcoin Gold double-spending totaled over $70,000. Cryptocurrencies with large participation ratios, such as Bitcoin, are less threatened. This is because, with today's mining technology, it is almost impossible for attackers to access such processing power. But regardless, blockchain networks need to take high-level security measures to protect against these attacks.

How to Avoid a 51% Attack?

The 51% attack is considered a threat to the security of blockchain networks, and many blockchain networks have developed various security protocols to counter this type of attack. These include protocols that prevent attacker control by dividing the network's hash power and preventing attackers from double-spending by performing transaction verification.