An improved technique utilizes a honeypot-style seeding of synthetic user identifiers which, if used by spear-phishing intruders, enable easy discovery of the intruders. Along these lines, an administrator of a network constructs false employee profiles on a social network with the intent of intercepting any email to that employee. Such employee profiles correspond to no actual employee of the corporation, but are in fact synthetic entities designed to appear to be an actual employee. These profiles contain identifiers that describe the employee, such as a name, position within the corporation, telephone number, educational background, past positions, and social connections. The administrator configures a receiver at the corporate network to block from entering the secure network emails that include references to any of these identifiers.