Aglets, a framework and runtime platform for mobile agentsdeveloped by the IBM Tokyo Research Laboratory, is an advanced systemof mobile agents written in Java, and is already used in somecommercial applications. Using mobile agent technologies providespotential benefits to applications, but they also pose securitythreats to those applications. These threats not only come asmalicious agents, but also in the form of malicious hosts. In thispaper we introduce security features against these threats.