The reuse of a single Maritime Mobile Service Identity (MMSI) by multiple vessels is a serious threat to maritime safety, undermining collision avoidance and search and rescue efforts. To combat this, we propose an algorithm that detects MMSI reuse by analyzing AIS message broadcast frequencies. Our method first identifies potential reuse suspects by filtering high-quality AIS signals and comparing their minimum broadcast interval to the theoretical standard. These suspects are then subjected to a secondary confirmation process, which validates the anomaly by examining the count and average interval of static messages over a 10-h period for a definitive judgment. Simulations confirm the algorithm’s high efficiency and accuracy in identifying MMSI reuse, providing a robust, automated technical solution for maritime regulatory bodies.