Design Fraud Detection

1. Frame the Problem: The Opponent in the Loop

"Design fraud detection for a payments platform." This question does not use the funnel at all. There is no catalog to narrow down. There is just a stream of transactions, and each one needs a decision in tens of milliseconds, while the payment is held, waiting for your answer.

Here is the ingredient no other lesson in this module has: an adversary. A recommendation system's users do not study your ranker in order to defeat it. Fraudsters do exactly that, professionally. Every pattern your model learns starts expiring the moment it ships