What does the dirty flag mean in a FortiGate session configured for NGFW policy mode?

What does the dirty flag mean in a FortiGate session configured for NGFW policy mode?

A. The existing session table entry has been updated with the app_id and the firewall policy table needs to be checked for a match. B. The application or URL category is unknown and needs to be rescanned by the IPS engine to try to identify the Layer 7 details. C. The URL category for this session has been updated by FortiGuard and the session needs to be checked against the policy again to ensure proper web filtering is applied. D. Traffic has been identified as coming from an application that is not allowed and the relevant replacement message needs to be displayed to the user, if configured.