In light of a recent investigation, Jared, a security engineer at a manufacturing company, discovered that an engineer's compromised workstation was being utilized to establish connections with SCADA systems even when the engineer was not logged in. Since the engineer holds the responsibility of administering the SCADA systems and cannot be restricted from accessing them, what step should Jared take to mitigate this threat?

The most appropriate step to mitigate the threat in this scenario is to implement account usage auditing on the SCADA system. This will allow Jared to track all activity on the SCADA system, even when the engineer is not logged in. This will help to identify any unauthorized activity and take steps to remediate it.
Implementing an NIPS (Network Intrusion Prevention System) on the SCADA system would also be a helpful step, as it could detect and block malicious activity in real time. However, NIPS can be expensive and difficult to manage, so they may not be practical for all organizations.
Installing host-based antivirus software on the engineer's system would not be effective in this scenario, as the malware is already on the system. However, it is still a good practice to have antivirus software installed on all workstations, as it can help to prevent future infections.
Using FDE (Full Disk Encryption) on the engineer's system would also not be effective in this scenario, as it would not prevent the malware from accessing the SCADA system. However, FDE can be a good way to protect sensitive data on laptops and other portable devices.