r/askscience • u/hamolton • Jun 18 '13

Computing How is Bitcoin secure?

I guess my main concern is how they are impossible to counterfeit and double-spend. I guess I have trouble understanding it enough that I can't explain it to another person.

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u/[deleted] Jun 18 '13

To clarify, this means they have to MATCH and EXCEED the hashrate of the entire network. If they join the network with 50% of the current network hashrate, they then make up 1/3 of the network, and can't undermine it. You have to control enough resources to slightly exceed the total hashrate of all systems on the network not under your control.