51% Attack

A 51% attack is a potential attack on a blockchain network, where a group of miners control more than 50% of the network's mining hash rate, or computing power. This majority control theoretically gives the attackers the power to alter the blockchain. They could prevent new transactions from gaining confirmations, allowing them to halt payments between some or all users. They could also reverse transactions that were completed while they were in control, potentially allowing them to double-spend coins. However, changing historical blocks-transactions locked in before the start of the attack-would be extremely difficult even in the event of a 51% attack.

Here are some examples of 51% attacks that have occurred:

• Bitcoin Gold (BTG): In 2020, the Bitcoin Gold blockchain experienced two 51% attacks. In the first attack, 14 blocks were removed from the network and 13 new blocks were added, resulting in 1,900 BTG coins being double-spent. In the second attack, 15 blocks were removed and 16 were added, with 5,267 BTG being double-spent. The total loss was approximately $72,000.
• Ethereum Classic: This is another example of a project that has suffered a 51% attack.
• Verge: Verge is also among the projects that have experienced a 51% attack.

Please note that while a successful attack on major networks like Bitcoin or Ethereum is unlikely due to their large participation rate, smaller networks are more frequent targets for 51% attacks. It's also worth noting that a 51% attack is a very difficult and challenging task, and in most cases, the group of attackers would need to be able to control the necessary 51% and have created an alternate blockchain that can be inserted at the right time.