This is a quote from the book "On Zero Confirmation Transactions" by Chris Pacia
...es below a certain value, while ShapeShift continued to accept them.
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The fact that ShapeShift failed to stay up-to-date with changes in miner policy, and paid a small price for doin
g so, is hardly evidence of unconfirmed transactions being ‘trivially double spent’ or ‘always unsafe’. Yet the opportunity was not missed to push that propaganda on everyone.
Up to this point we have been considering a network where all miners are using the “first-seen” policy or variations thereof. In such a network, we can ...