Senior interview questionAsked at PayPal · interview write-up
Design a real-time account-takeover model inside payment authorization, handling delayed noisy labels, feature freshness and a tight latency budget.
Model answer
Score at login and payment within tens of milliseconds. Features: device fingerprint, session behaviour, recent credential or address changes, and velocities, served from a streaming feature store and logged at decision time so training sees exactly what serving saw.
Labels arrive late and noisy, from chargebacks and customer reports, so train on matured windows plus faster proxies like failed step-up challenges. Rather than only block, pick actions by risk: allow, step-up authentication or hold, with thresholds set on expected loss, and a rules fallback on timeout.
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