> There exists a particular anti-fraud heuristic at a YC company. They shared it to me in confidence, because as soon as you know it exists, you can trivially avoid it. I mean trivially. It's apparently insanely effective, though, half because it has a really good handle on who it wants to frustrate and the other half because it's not in the literature at all and, as a consequence, the bad guys don't even know they have to avoid defenses in that class of algorithms.

Please don't tell me its capitalization of the cardholder name...