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.