This is a quote from the book "On Zero Confirmation Transactions" by Chris Pacia
...hat passes, however, the more difficult it becomes to reverse a transaction. Typically we say that “unconfirmed” transactions are the easiest to reverse, while the deeper a transaction is in the blockchain, the more difficult it is to reverse. After a transaction is buried six or so blocks deep in the blockchain (about an hour), the probability of a successful double spend drops cl ose to zero.

But why all the fuss about about unconfirmed transactions? While most Bitcoin users can afford to wait an hour for their payments to confirm, there are some business mo...
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