In finance and healthcare, event processing systems handle sensitive data on behalf of many clients. Guaranteeing information security in such systems is challenging because of their strict performance requirements in terms of high event throughput and low processing latency.

We describe DEFCON, an event processing system that enforces constraints on event flows between event processing units. DEFCON uses a combination of static and runtime techniques for achieving light-weight isolation of event flows, while supporting efficient sharing of events. Our experimental evaluation in a financial data processing scenario shows that DEFCON can provide information security with significantly lower processing latency compared to a traditional approach.