one of the key strengths of Bitcoin and blockchain technology is their distributed way of building and verifying data that the centralized network of nodes ensures the protocol rules are being followed and that all participants agree on the current state of the blockchain the proof-of-work consensus algorithm is what assures that miners are only able to validate a new block of transactions if the network nodes collectively agree on the validity of that block a – performance is based on the amount of computational power they have and this is usually referred to as hash rate or hashing power the mining power is distributed over different nodes across the world which means it is not in the hands of a single entity at least it is not supposed to be but what happens when the hash rate is no longer distributed when enough what happens if one single entity is able to obtain more than 50% of the hashing power one possible consequence of that is what we call a 51% attack also known as a majority attack a 51% attack it’s a potential attack on a blockchain network where a single entity or organization is able to control the majority of the hash rate potentially causing a network disruption in such a scenario the attacker would have enough mining power to intentionally exclude or modify the ordering of transactions they could also reverse transactions they made while being in control leading to a double spending problem a successful majority attack could also allow the attacker to prevent some or all transactions from being confirmed or to prevent miners from mining resulting in what is known as mining monopolies on the other hand a majority attack would not allow the attacker to reverse transactions from other users nor to prevent transactions from being created and broadcasted to the network changing the blocks reward creating coins out of thin air or stealing coins that never belonged to the attacker are also not possible how likely is a 51% attack since a blockchain is maintained by a distributed network of nodes all participants cooperate in the process of reaching consensus the bigger the network the stronger the protection against attacks and data corruption and that is why Bitcoin is considered the most secure blockchain several early miners joined the Bitcoin network to contribute to its growth and security with the rising price of Bitcoin as a currency new miners entered the system aiming to compete for the block rewards such a competitive scenario is one of the reasons why Bitcoin is secure miners have no incentive to invest large amounts of resources if it is not acting honestly and striving to receive the block reward therefore a 51% attack on Bitcoin is rather unlikely due to the magnitude of the network once a blockchain grows large enough the likelihood of a single personal group obtaining enough computing power to overwhelm all the other participants rapidly drops to very low levels also changing previously confirmed blocks gets more and more difficult as the chain grows because the blocks are linked and it is only possible to change a certain block if all subsequent confirmed blocks are discarded for the same reason the more confirmations a block have the higher the costs for altering or reverting transactions therein hence a successful attack would probably only be able to modify the transactions of a few recent blocks for a short period of time and even if a malicious entity is not motivated by profits and manages to successfully perform a 51% attack the Bitcoin protocol would be quickly adapted as a response as the biggest blockchain network Bitcoin is very resilient to attacks and is considered the most secure and reliable cryptocurrency to learn more about crypto currencies and the technologies behind them don’t forget to watch our other videos at finance academy