System designHardsd-g588

Subject Ml fraud detectionLevel Senior–Staff~55 minCommon in ML systems · Distributed systems interviewsIndustries Technology

Question

Design a real-time fraud-detection system for a payments platform processing 5k transactions/sec, where each transaction must get a risk score within a 100ms p99 budget to allow/deny/challenge. Fraud is rare (<0.5%), labels arrive days later via chargebacks, and adversaries adapt continuously. Cover the feature pipeline (including velocity/aggregate features), the model and decision layer, and how you keep up with evolving fraud patterns.

What a strong answer looks like

Clarify scale and constraints first. Propose a clean component breakdown, then go deep on the hard parts — data model, bottlenecks, consistency, failure modes — and name the trade-offs you are making.

Learn the concepts

Narrate your design

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Run or narrate your approach, then ask the coach.