This is a quote from the book "On Zero Confirmation Transactions" by Chris Pacia
... out the store with the merchandise, then send the double spend to the Eligius pool. At the time of writing Eligius has about 3% of the hashing power. That means you have a 3% chance that Eligiu
s will mine the next block containing your double spend. A 3% chance of success is still fairly low, but you can repeat this over and over again until it works.
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As damning as this s
eems to zero confirmation transactions, this too is detectable. The sys admin in charge of the retailer’s POS software could just add his own “is notorious” check to incoming transactions ...