IEC/TR 62541-2:2010(E) describes the OPC Unified Architecture (OPC UA) security model. It describes the security threats of the physical, hardware and software environments in which OPC UA is expected to run. It describes how OPC UA relies upon other standards for security. It gives an overview of the security features that are specified in other parts of the OPC UA specification. It references services, mappings, and profiles that are specified normatively in other parts of this series of standards. It is directed to readers who will develop OPC UA client or server applications or implement the OPC UA services layer.