A new helpdesk employee at a multinational corporation took it upon himself to test the security of the servers that holds highly confidential information regarding specific government projects. Which

Warning banners deter unauthorized logical or remote access attempts but do not physically prevent an employee from walking into an unsecured server room.

Physical access controls such as badge readers, biometrics, or locked server room doors directly prevent unauthorized personnel - including employees like helpdesk staff - from reaching hardware that stores confidential data. This is the foundational physical security control (mapped to NIST PE-3) specifically designed to limit who can physically interact with critical systems.

A mantrap with a manned guard is a more advanced and costly physical control; secured and controlled access is the more standard well-known deterrent referenced in this context.

Reviewing the Acceptable Use Policy is an administrative awareness control but does not physically restrict or deter access to the server room.