One embodiment of the present invention provides a system for detecting insider attacks in an organization. During operation, the system collects data describing user activities. The system extracts information from the data that includes user information and user communications. The system then generates a topic-specific graph based on the extracted information. The system analyzes a structure of the graph to determine if one or more rules have been violated. The system may determine that a rule associated with the graph has been violated and signal an alarm in response to detecting the rule violation.