Security is a major issue for mobile components that roam the Internet. When downloading a software component from the Internet, it is often impossible to decide in advance if this piece of code should be considered as safe or potentially dangerous for the local system. With the JAMUS (Java Accommodation of Mobile Untrusted Software) platform we tackle these problems based on a contractual approach of resource management and access control. JAMUS can accommodate mobile Java components, provided that these components can specify their requirements regarding resource utilisation in both qualitative and quantitative terms.