Detecting massive network events like worm outbreaks in fast IP networks, such as Internet backbones, is hard. One problem is that the amount of traffic data does not allow real-time analysis of details. Another problem is that the specific characteristics of these events are not known in advance. There is a need for analysis methods that are real-time capable and can handle large amounts of traffic data. We have developed an entropy-based approach, that determines and reports entropy contents of traffic parameters such as IP addresses. Changes in the entropy content indicate a massive network event. We give analyses on two Internet worms as proof-of-concept. While our primary focus is detection of fast worms, our approach should also be able to detect other network events. We discuss implementation alternatives and give benchmark results. We also show that our approach scales very well.