A 51% attack is a potential attack on a blockchain network where an individual or a group of individuals control more than 50% of the network’s computing power. This allows them to gain control of the network and manipulate its transactions, including double-spending coins or blocking transactions from other users.
In a blockchain network, transactions are verified and added to the blockchain by a network of computers, called nodes, through a consensus mechanism. The most common consensus mechanism is Proof of Work, where nodes compete to solve a complex mathematical problem, and the first one to solve it gets to add the next block of transactions to the blockchain.
If an individual or a group of individuals control more than 50% of the network’s computing power, they can create a longer chain of blocks faster than the rest of the network, making their chain the longest and the valid one. This gives them the power to reverse or modify transactions, double-spend coins, or even block other users from making transactions.
A 51% attack is considered a serious threat to the security of a blockchain network, and it’s usually prevented by increasing the network’s computing power and decentralization.