Quote from: temp1029 on February 25, 2011, 03:57:35 PM

Quote from: emansipater on February 25, 2011, 03:12:03 AM

We do have a historical precedent of how the community tends to respond: in block 74638, or alternatively on August 15, 2010, someone exploited a loophole in the then-current client to give themselves 184 billion bitcoins. An update to the Bitcoin software was immediately created that deleted that block and corrected the blockchain while including all other legitimate transactions (the cryptographic security of bitcoin makes it easy to keep valid transactions in these scenarios), and that new version of software was released to the public. The majority of the nodes switched immediately for obvious reasons, and the fixed blockchain overtook the compromised one at block 74691 (very quickly). This is also an excellent demonstration of why simply trusting the most computationally intensive blockchain is a safe move--once a clear majority of computing power has switched that blockchain will always win out to become the most secure record. And even in the midst of this commotion an attacker with more computational power than the whole network couldn't have spent other people's coins or altered their transactions. It also demonstrates how Bitcoin's nature allows anyone connected to the network to hold it accountable. Go jgarzik!

Just to make sure I understand this last bit, that person could still have all 184 billion Bitcoins, but they would not be considered valid by any Bitcoin user who has updated to the new version, correct?

Right! (I changed the one word above and bolded the first one because I'm pretty sure that's what you meant: "not valid") Talking in terms of currencies you could say that billionaire person is in Bitcoin 2.0 already while we are all in Bitcoin Original. They can't sell their Bitcoins on our exchanges or exchange them with our software--if they wanted to use them they would have to find some poor fool to join their side of things and leave ours. Or if you want you could flip those terms--the point is that each person gets to decide which currency they're using, and nobody can force them to change if they don't want to, not with the biggest supercomputer in the world. This is actually a much stronger position than real world cash!

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Thank you guys so much for the wonderful and timely explanations, this thread has made me a "believer".

Result: bitcoinUserCount++; Wink

Excellent! You are very welcome.