Fraud Detection System

Let me walk you through how I'd design a fraud detection system in production/PayPal scale. I'll go stage by stage – business and ML objectives, high-level design, data and feature strategy, embeddings, pipeline architecture including modeling and training details, infrastructure, evaluation, and robustness. Fraud detection is unique because it's adversarial by nature, requires real-time decisions with massive consequences, and operates under extreme precision requirements to avoid harming legitimate users.