This is a quote from the book "On Zero Confirmation Transactions" by Chris Pacia
...ude double spend in their blocks. This can be done with a very high success rate and is probably responsible for almost all of the ‘zero confirmations transactions are trivially reversed’ me me.

Well not so fast

While we can indeed double spend unconfirmed transactions with a very high success rate, the merchant should be able to trivially detect mos
t double spend attempts as they happen. Last year Gavin Andresen and Tom Harding wrote some patches for Bitcoin Core that would have relayed the first double spend attempt for each transaction a...
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