There is an increasing demand for security mechanisms for mobile devices that will be able to control execution of different interacting applets in a concurrent environment. An analysis of the security requirements for the booming domain of mobile games [4] shows that to capture some of the requirements we need to introduce a notion of session. A session accumulates all events that occur in the application since we have started it and until it is terminated. Then we can aggregate the constraints into two large classes: constraints on the current session and constraints across multiple sessions of the application (or its interaction with other applications).