This is the username or identity of a user among those with the most blocked requests. An admin uses this to identify a specific individual who may either be deliberately attempting to bypass acceptable-use policy or whose machine is compromised and auto-generating blocked traffic, for example malware calling out to blocked command-and-control domains, which determines whether the follow-up is an HR conversation or an incident-response investigation. For example, one username accumulating an unusually high blocked count with categories like malware or command-and-control rather than social media would point toward a compromised endpoint rather than casual policy violation.