Today, we face a growing interest in distributed business-to-business applications using the Internet as communication media. However, the involved security threats are often neglected in the design of such systems. In this paper, we present our security architecture for an Internet based virtual trading community. Our solution has been designed for an heterogeneous, distributed workflow management system environment which we call WISE (Workflow based Internet Services). The modular security services toolbox and the group key management form the core of the security architecture. Furthermore, we do not interfere with local security policies. We rather reuse the defined roles by mapping them to security communication parameters. So, we are able to present a scalable, secure solution for cooperative work over the Internet.