What classification indicates that unauthorized disclosure could cause serious damage to national security?

The classification that indicates unauthorized disclosure could cause serious damage to national security is the Secret Classification. This classification is used for information that, if disclosed without authorization, could harm national security interests significantly.

In the classification system, information is categorized into levels based on the potential damage that could arise from unauthorized access. Secret information is one level above Confidential, which protects information that could cause damage but not to the severe extent designated for Secret material. The Top Secret classification represents information that, if disclosed, could cause exceptionally grave damage to national security, making it the highest classification level.

The concept of Restricted is generally not used in the U.S. national security classification framework, as it does not reflect the severity of damage that can occur if such information is disclosed. Therefore, Secret Classification serves as the appropriate designation for information requiring a higher level of control to protect national security interests.