51% attack
A 51% attack lets one miner control most of a blockchain’s power—enabling double spending and invalidating honest transactions.
When the mining reward is low, it is logical that only a few miners validate blocks.At this point, a miner can easily hold 51% of the network's computing power.This is when a 51% attack occurs.The miner can then start mining fraudulent transactions, such as double spending, and invalidate other transactions.
