Security, scalability, and performance are critical for large-scale component-based applications. Weaving security solutions into the fabric of component-based architectures often worsens the scalability and performance of the resulting system. In this paper we analyze the sources of nonscalability and conduct an empirical study that shows that close to 80% of interactions between components and their clients in different commercial systems occur within protected security boundaries. Based on these findings we propose a novel scalable security mechanism for component-based systems called Component Adaptive Scalable Secure Infrastructure Architecture (CASSIA). CASSIA utilizes the topology of the security boundaries and patterns of interactions among components to achieve noticeable improvements in scalability and performance for component-based applications. We conduct a case study that confirms the scalability of CASSIA, and propose a Secure COmponent Protocol (SCOP) that incorporates our mechanism into a component infrastructure.