Many complex systems display a surprising degree of tolerance against errors.
For example, relatively simple organisms grow, persist and reproduce despite drastic pharmaceutical or environmental interventions, an error tolerance attributed to the robustness of the underlying metabolic network 1 . The stability of these and other complex systems is often attributed to the redundant wiring of the functional web defined by the systems' components. We find that such networks display an unexpected degree of robustness, the ability of their nodes to communicate being unaffected even by unrealistically high failure rates. Such error tolerance and attack vulnerability are generic properties of communication networks. The increasing availability of topological data on large networks, aided by the computerization of data acquisition, had led to great advances in our understanding of the generic aspects of network structure and development 9-16 .