This case study describes and analyzes a breach of the confidentiality and integrity of personally identified health information (e.g. appointment details, answers to patient's questions, medical advice) for over 800 Kaiser Permanente (KP) members through KP Online, a web-enabled healthcare portal. The authors obtained and analyzed multiple types of qualitative data about this incident including interviews with KP staff, incident reports, root cause analyses, and media reports. Reasons at multiple levels account for the breach, including the architecture of the information system, the motivations of individual staff members, and differences among the subcultures of individual groups within as well as technical and social relations across the Kaiser IT program. None of these reasons could be classified, strictly speaking, as "security violations." This case study, thus, suggests that, to protect sensitive patient information, healthcare organizations should build safe organizational contexts for complex health information systems in addition to complying with good information security practice and regulations such as the Health Insurance Portability and Accountability (HIPAA) of 1996.