A manufacturing company is having issues with unauthorized access and modification of the controls operating the production equipment. A communication requirement is to allow the free flow of data…

SCADA security measures are a broad category of controls relevant to industrial environments, but the question asks for the best single remediation for access and modification control, where AAA is more precise and direct.

A NIPS (Network Intrusion Prevention System) can block known attack patterns in transit but does not authenticate or authorize users, meaning a legitimate but unauthorized insider could still modify controls.

AAA enforces Authentication to verify identity before granting access, Authorization to restrict which users can modify production equipment controls, and Accounting to log all actions for auditing and forensics. This directly remediates both unauthorized access and unauthorized modification without restricting the free flow of data between network segments, satisfying the stated communication requirement.

Restricting access to a single management station via firewall would contradict the explicit requirement to allow the free flow of data between all network segments at the site.