We present Spy@Runtime, a tool to infer and work with behavior models. Spy@Runtime generates models through a dynamic black box approach and is able to keep them updated with observations coming from actual system execution. We also show how to use models describing the protocol of interaction of a software component to detect and report functional changes as soon as they are discovered. Monitoring functional properties is particularly useful in an open environment in which there is a distributed ownership of a software system. Parts of the system may be changed independently and therefore it becomes necessary to monitor the component's behavior at run time.