Designing a secure and reliable mobile agent system is a difficult task. The agent operating system (AOS) is a building block that simplifies this task. AOS provides common primitives required by most mobile agent middleware systems, such as primitives for secure communication, secure and tamper-evident agent packaging and agent migration. Different middleware processes can use AOS at the same time; effective security mechanisms protect AOS resources owned by different middleware processes. Designed as a portable and language-neutral middleware layer residing between the mobile agent system and the operating system, AOS facilitates interoperability between agent platforms and between different implementations of AOS itself. AOS has been imp...