The increasing potential to interconnect and combine the computational power of devices with different capabilities and purposes leads to new security issues. While security is nowadays defined as the possibility to prevent “negative things from happening”, security of the future focuses on the potential of new vulnerabilities in software being exploited due to the increased exchange of mobile code, and the inclusion of context and location in services. For new services to be accepted, it is necessary to manage a constantly changing environment. Security issues, as well as privacy and trust concerns, pose a number of obstacles for the acceptance of emerging services. It is argued here that present-day security is inadequate due to the conceptional backgrounds guiding the development of security mechanisms.