Security is one of the most essential quality attributes of distributed systems, which often operate over untrusted networks such as the Internet. To incorporate security features during the development of a distributed system requires a sound analysis of potential attacks or threats in various contexts, a process that is often termed threat modeling. To reduce the level of security expertise required, threat modeling can be supported by threat libraries (structured or unstructured lists of threats), which have been found particularly effective in industry scenarios; or attack taxonomies, which offer a classification scheme to help developers find relevant attacks more easily. In this paper we combine the values of threat libraries and taxonomies, and propose an extensible, two-level pattern-based taxonomy for (general) distributed systems. The taxonomy is based on the novel concept of a threat pattern, which can be customized and instantiated in different architectural contexts to define specific threats to a system. This allows developers to quickly consider a range of relevant threats in various architectural contexts as befits a threat library, increasing the efficacy of, and reducing the expertise required for, threat modeling. The taxonomy aims to classify a wide variety of more abstract, system- and technology-independent threats, which keeps the number of threats requiring consideration manageable, increases the taxonomy's applicability, and makes it both more practical and more useful for security novices and experts alike. After describing the taxonomy which applies to distributed systems generally, we propose a simple and effective method to construct pattern-based threat taxonomies for more specific system types and/or technology contexts by specializing one or more threat patterns. This allows for the creation of a single application-specific taxonomy. We demonstrate our approach to specialization by constructing a threat taxonomy for peer-to-peer systems. © 2013 Elsevier B.V.