Bitcoin Forum

BlockCypher provides Bitcoin wallet services to larger organizations such as exchanges and payment providers. During the recent fracas of "dust" transactions crowding the Bitcoin network, one of their larger clients, Erik Voorhees' ShapeShift.io, suffered a double-spend attack amounting to 2.6 BTC.

The biggest offering of BlockCypher is what they call a "Confidence Factor" which basically means what it sounds like – if the processor is reasonably sure (as in more than 99%) that a double-spend will not be attempted, the transaction is processed with zero confirmations. BlockCypher describes their method like so:

In simpler terms, if an unconfirmed transaction returns a confidence factor of 99.9%, then our data says there's a 0.1% chance that an attempted double-spend will succeed. By design, we're conservative. Even when we return 90% confidence, the likelihood of a successful double-spend is significantly lower than 10%.

https://www.cryptocoinsnews.com/blockcypher-zero-confirmation-bitcoin-transactions-still-viable/ (https://www.cryptocoinsnews.com/blockcypher-zero-confirmation-bitcoin-transactions-still-viable/)