Transition to Web3 - Course 1 | Blockchain Basics
They can also cooperate to falsify
If the majority of computers working on the blockchain are honest and they’re not organized together to change the data, a bad actor won’t be able to manipulate the data. They’ll have no way to catch up with the speed of the longest blockchain and their blockchain will not be valid.
What happens if the majority of computers (at least 51%) are coordinated with each other and they know exactly which data to manipulate? Then, they can solve the puzzles faster, build a longer chain and create an alternate truth. This is one of the ways to 'hack' a blockchain (also called a 51% attack).