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What Is a 51% Attack
An attack of 51% refers to the ability of a group of miners to control a large number of transactions on a network such as the Bitcoin blockchain without the consent of the majority of its users. An attacker could prevent new transactions from receiving a confirmation that would allow them to stop payments to a user. In Bitcoin's blockchain, this attack is still hypothetical, and it would almost certainly not be possible to create new coins or swap old blocks. However, there is the possibility of reversing transactions made on the controlled network - which means that the issuance of coins could be doubled.
If an attack proves highly damaging, it could destroy a currency and its currency, such as Bitcoin, in the short term.
How a 51% Attack Works
Bitcoin and other cryptocurrencies are based on the blockchain, a form of distributed ledger. This digital file records all transactions made on a cryptocurrency network and is available for verification by users and the public.
As the name implies, the blockchain is a chain of blocks that are bundles of data, and each transaction is completed within a certain period of time. Bitcoin creates a new block every 10 minutes, and as a result, no one can issue coins twice.
Once the block is finished and dismantled, it cannot be changed, as network users would quickly detect and reject fraudulent versions of the public register. However, if an attacker or group of attackers controls the majority of the computing power on the network, they can interfere with the process of adding a new block.
They can block other users "transactions and prevent other miners from completing blocks, which theoretically allows them to monopolize the extraction of new blocks and earn a reward. Currently 12.5 new Bitcoins are being created, but these will eventually fall to zero. If it looks like you have a few coins left that you just spent, you can cancel your transaction and return them.
Known as "double spending," this vulnerability is a fundamental cryptographic hurdle that the blockchain should overcome. A network that allowed spending to double would therefore quickly lose confidence in itself.
On the other hand, another form of attack is possible, but it is extremely difficult to change a transaction that was completed before the attack. It would be impossible to change the transaction at a checkpoint where the software in Bitcoin is hard - encrypted. The further back the transactions are, the more difficult it would have been to change them, and it is initially impossible to change them after the transactions have been completed.