We describe a novel framework for early detection and isolation of security violations in heterogeneous environments, based on real-time service hopping. In distributed client-server systems, service hopping fills a role analogous to frequency-hopping spread-spectrum techniques for secure wireless communication. The framework incorporates design principles for secure hopping, as well as engineering principles for improving throughput in the presence of a statistically noisy interconnection network. We describe potential large-scale applications of the hopping techniques, and present some initial experimental results with a hopping client-server system.