Fraud detection

How this question breaks down

1. 1SignalsCore24 minDecide what counts as fraud and when you can know it, then build the signals that separate a stolen card from a good customer, from a single payment's details up to rings of accounts that share cards and devices.
2. 2Real timeCore28 minScore every payment inside the checkout in under 75 ms, keep velocity counters that count the burst in progress, and turn a probability into allow, challenge, review or block by pricing each mistake.
3. 3AdversariesCore22 minFraudsters read your declines and change within hours while labels take weeks; cover the gap with fast rules and anomaly alarms, keep learning from the payments you block, and let emergency rules expire.

Work through the parts in order and you’ve covered the full design. Each part is one topic.