It's actually not all that hard and doesn't require timing more precise than a few seconds. You can try it yourself: https://blockchain.info/create-double-spend

It's actually not all that hard and doesn't require timing more precise than a few seconds. You can try it yourself: https://blockchain.info/create-double-spend https://blockchain.info/create-double-spend That site isn't great because it's tricky to hit the two submit buttons in succession, but a fairly trivial script can do the same thing without much difficulty. The reason why you don't hear about it is in reality there pretty much aren't any services out there that are actually vulnerable to that kind of double-spend in a way that results in genuine financial loss. Aside from some rare exceptions everyone accepting zero-conf transactions are either selling something that can be recalled after the fact, (tell the shipping department to stop) or has zero marginal cost. (like mp3s)