Many real-time distributed computing (RTDC) applications have stringent action timing requirements as well as tight security-enforcement requirements. Integration of security enforcement mechanisms into advanced component-based RTDC schemes has been recognized as an important research topic in recent years. In this paper we propose the first formal extension of the Time-triggered Message-triggered Object (TMO) component model devised to facilitate efficient construction of secure RTDC applications. The newly extended TMO structure is called the Adaptive Secure TMO (AS-TMO). A distinguishing characteristic of the proposed scheme is that security attributes (e.g., roles) are associated with AS-TMO parts (e.g., methods and data-container variable groups) instead of with entire AS-TMOs. We also present the execution engine facilities being incorporated into the middleware model, the TMO Support Middleware (TMOSM), for providing the security-enforcement capabilities defined in the AS-TMO scheme.