The recent years of development in mobile computing as powerful handheld computers and high-speed wireless networks creates opportunities for new user-groups in the mobile workforce to take advantage of mobile technologies. User-groups may be more or less geographical distributed and as a consequence more or less marooned when it comes to obtaining IT/IS support and this increases the complexity of delivering IT/IS support to these geographically distributed end-users. In this design paper the aim is to develop a design theory to manage problems in IT/IS support to the outbound user. Semistructured interviews were performed with developers and documents studies of an information system comprising handheld mobile computing devices for drivers. From the interviews, a design theory based on the implemented strategy of defensive design is presented. The six components of IS design theory by Gregor and Jones is applied as a theoretical framework for evaluation of the design theory.