This paper describes a mobile agent platform, Secure Mobile Agent Platform (SECMAP), and its security infrastructure. Unlike other agent systems, SECMAP proposes a new agent model, the shielded agent model, to meet security requirements and provides functionalities which ensure the implementation of the the shielded agent model. It provides secure agent communication and migration facilities, and maintains security policy information to examine agent actions and to prevent undesired/unauthorized activity, while employing cryptographic techniques to meet security constraints.