user11296: I've heard discussion that if you have 51% of the network's hash power, you can effectively accept or reject any changes to the blockchain (and therefore create undeserved gain for yourself).
Has anyone ever accomplished this? It's theoretically possible, but has it been done?

user11297: This research done at Cornell seems to suggest it is easier than expected but doesn't speak to the fact that it has or hasn't been done.
http://arxiv.org/abs/1311.0243

user-1: I think it is safe to assume that the creator once had full control of the blockchain. And at the beginning, there probably were times when someone had 51% hash power.
However, those people would have no incentive to perform an attack, so my guess would be that it has not happened yet.

11296: <p>I've heard discussion that if you have 51% of the network's hash power, you can effectively accept or reject any changes to the blockchain (and therefore create undeserved gain for yourself).</p>

<p>Has anyone ever accomplished this? It's theoretically possible, but has it been done?</p>
 11297: <p>This research done at Cornell seems to suggest it is easier than expected but doesn't speak to the fact that it has or hasn't been done.</p>

<p><a href="http://arxiv.org/abs/1311.0243" rel="nofollow">http://arxiv.org/abs/1311.0243</a></p>
 -1: <p>I think it is safe to assume that the creator once had full control of the blockchain. And at the beginning, there probably were times when someone had 51% hash power.</p>

<p>However, those people would have no incentive to perform an attack, so my guess would be that it has not happened yet.</p>
