nodes and miners

[MarkRoberts]

Besides the users, there are two major players in Bitcoin: nodes and miners.

Nodes are the rule enforcers. Nodes check transactions and blocks, and relay valid ones. Nodes are run by users to make sure miners work as intended.

Miners are the workers / service providers. Miners compute and generate blocks according to the rules set by nodes. Miners normally run a node for quick update of the blockchain's status.

In order to attack the network (or cheat), the attacker must gain control of 51% of the mining power. The security of Bitcoin can be measured by the total amount of the mining power, aka, hashrate.

Now, to answer your original question, there was an estimation in 2015 that the total hashrate of Bitcoin network was 8 times the combined speed of the world's 500 fastest supercomputers. The hashrate today is an order of magnitude higher. It's not impossible for super rich people or states to beat the hashrate, but it would cost a lot. If/when that happens, there is still the option for the users to change the hash algorithm. So it's very unlikely someone will build so many miners to try and defeat Bitcoin.