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.
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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...