There is even some evidence that double-spending attacks have already happened. You don't strictly speaking need 51%, that majority just ensures that your chai

There is even some evidence that double-spending attacks have already happened. You don't strictly speaking need 51%, that majority just ensures that your chain will win out over time. The original bitcoin paper[1] details the probabilities involved for nodes controlling < 51%, if anyone is interested it is a short and good read. It could be even worse than that however. Another post on BCT[2] talks about a "time warp attack", where at 51% node could effectively mine all remaining bitcoins in one fell swoop. [1] http://bitcoin.org/bitcoin.pdf http://bitcoin.org/bitcoin.pdf [2] https://bitcointalk.org/index.php?topic=114751.0 https://bitcointalk.org/index.php?topic=114751.0