JavaSeal is a Java-based mobile agent system currently being developed in the context of the ASAP project. This paper offers a position statement on the requirements for JavaSeal's security infrastructure, and describes on-going and future work. Security in JavaSeal relies on two features: 1) the set of agents in the system is hierarchically structured: a parent agent intercepts the messages that its children exchange and can suppress them for security reasons, and 2) agents and their security policies are Java programs, and Java's strong typing semantics is the starting point for proving security properties of these programs.