Secure Lock is a legacy SCADAPack access feature kept for backward compatibility with older deployments. In practice, it provides an older way to authenticate or unlock device functions, but it is not the preferred modern access-control model.
In cyber security, legacy features like this matter because they can preserve weaker trust paths after newer controls are available. If Secure Lock is still enabled, an attacker who reaches the device may have another route to sensitive configuration or operational functions, especially if credentials are poorly protected. Defenders usually reduce that risk by replacing legacy access with role-based access control, limiting network reachability through segmentation, and firewalling RTU services so only approved management traffic can reach them. The goal is to shrink the attack surface and remove outdated access methods before they become a liability.