A 51% attack refers to a vulnerability in a blockchain network where an individual or group gains control of more than 50% of the network's mining power (hash rate). This allows the attacker(s) to:
Prevent new transactions from being confirmed, effectively halting the network.
Reverse transactions that have already been confirmed, allowing them to double-spend coins.[1][3][4]
Some examples of 51% attacks include:
In July 2014, the mining pool ghash.io briefly controlled about 55% of the bitcoin network's computing power, though they voluntarily reduced their share to avoid a 51% attack.[1]
In 2016, the blockchains Krypton and Shift, which are based on Ethereum, suffered 51% attacks where the "51 Crew" group was able to acquire about 22,000 coins through double-...
