This is a quote from the book "On Zero Confirmation Transactions" by Chris Pacia
...r for their transaction to confirm. If retailers are unable to mitigate the risk of fraud when accepting unconfirmed transactions, then they simply wont accept Bitcoin.


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w to double spend

Double spending an unconfirmed Bitcoin transaction is actually rather easy for people with the technical ability. The easiest way is to create two transactions which spend the same Bitcoins. The first transaction sends the coins to the merchant, while the second sends the coins back to yourself. The trick here is you need to make sure the merchant see...
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