Fraud detection is critical for identifying and mitigating fraudulent activities in real-time by analyzing data patterns, behaviors, and anomalies. It encompasses three primary methods: rule-based systems, statistical methods, and machine-learning approaches, with the latter being the most prevalent due to its use of models like neural networks and clustering algorithms. The text explains how to build a real-time fraudulent click detection system specifically for click fraud in online ads, which involves generating fake clicks to inflate metrics. The system uses Python, Redpanda, and Apache Spark to process click data, flagging any session with three or more clicks on a URL within ten seconds as fraudulent. The architecture employs Redpanda for low-latency data handling and Apache Spark for scalable data processing, with the system's components structured to read, process, and distribute data across different Redpanda topics. The tutorial guides users through setting up the system using Docker, Python virtual environments, and Spark streaming, providing code samples and instructions for implementing the application and processing logic. As fraudulent methods evolve, integrating AI, machine learning, and real-time monitoring remains essential for enhancing fraud detection capabilities.