Best 15 OT Security Practices for Plant Managers – 2025 checklist

Why plant managers should care – short background

OT environments are built for safety and reliability, not security. As plants modernize (IIoT sensors, remote access, cloud analytics), attackers target OT to cause disruption, extortion, or physical harm. In response, guidance from NIST, CISA and IEC shows defenders must combine traditional safety-first thinking with cybersecurity controls tailored for OT’s uptime and latency constraints. Implementing security in OT is therefore a program – not a one-off project.

How to use this checklist

Treat the 15 items below as practical controls mapped to short, medium and long-term effort.
Focus first on controls that reduce exposure and risk without jeopardizing safety or production.
Use compensating controls (network isolation, monitoring) when you can’t patch immediately. Dragos and other OT leaders recommend defensive layering and prioritized hardening for resource-limited teams.

The 15 OT security practices (plant-manager friendly)

1. Build and maintain a complete OT asset inventory (hardware, firmware, software)

Why: You can’t protect what you don’t know. Inventory must include PLC/RTU models, firmware versions, network interfaces, serial devices, and dependencies. Use passive discovery where active scanning risks process disruption. Periodically validate against procurement and maintenance records. Dragos and CISA emphasize inventory as foundational. Action (30 days): Start a spreadsheet + passive scanning; tag critical assets and last-known firmware.

2. Network segmentation and microsegmentation (zone by function & risk)

Why: Segmentation reduces blast radius and prevents lateral movement. Implement Purdue-model zones (Enterprise ↔ Demilitarized Zone ↔ OT) and use strict access control between zones. Microsegmentation (where feasible) enforces policy per device/application. Ensure segmentation does not interfere with operator safety or control traffic timing. Action (60–120 days): Map flows, then apply ACLs/jump hosts for cross-zone connections.

3. Harden devices & remove default credentials

Why: Default accounts and insecure configs are common attack paths. Apply vendor hardening guides, disable unused services, change default passwords, and remove unnecessary software. Test in a lab first. Dragos recommends a hardening checklist for OT.

Action (30–90 days): Prioritize controllers and HMIs; document rollback steps.

4. Compensating controls for legacy systems (virtual patching & isolation)

Why: Many OT devices cannot be patched. Use compensating measures: network isolation, allow-lists, protocol proxies, and virtual patching at network level to block exploit vectors while preserving operations. Rockwell and other vendors recommend virtual patching where patches aren’t an option. Action (30–90 days): Deploy protocol-aware gateways and network-level rules for vulnerable devices.

5. Secure remote access (MFA, jump hosts, least privilege)

Why: Remote access is a high-risk vector. Use dedicated jump servers, MFA, session recording, strict RBAC, and time-boxed access. Avoid direct VPN access into OT zones. CISA’s guidance and industry practice demand hardened remote access architectures.

Action (30 days): Replace ad-hoc RDP/VNC with a controlled, audited jump host + MFA.

6. Identity & access management adapted to OT

Why: Apply least-privilege and unique operator identities – avoid shared accounts on controllers/HMIs. Where device constraints exist, control access via gateways, and ensure admins use separate admin workstations. Consider integrating with enterprise identity where latency/safety allows.

Action (60–120 days): Phase out shared accounts and implement RBAC for operators/maintenance.

7. Continuous monitoring & anomaly detection (OT-aware)

Why: Detecting lateral movement and process anomalies early prevents incidents. Use passive network monitoring and OT-aware IDS/EDR that understand Modbus, OPC, DNP3, etc. Feed alerts into your incident response playbooks. MITRE ATT&CK for ICS offers adversary tactics to align monitoring

Action (60 days): Deploy passive taps and baseline normal traffic for anomaly detection.

8. Patch management with safety-first testing

Why: Patching reduces vulnerability exposure but can break deterministic control logic. Test patches in staging, maintain rollback plans, and schedule maintenance windows. When immediate patching isn’t possible, apply virtual patches and segmentation. NIST’s OT guidance stresses conservative, test-driven patch processes.

Action (90+ days): Create a PLC/SCADA patch playbook with test criteria.

9. Secure supply-chain & firmware integrity

Why: Compromised third-party code and infected firmware are a rising risk. Track vendors, require secure development evidence (e.g., IEC 62443 supply chain practices), validate firmware images (checksums, signatures), and insist on SBOMs where possible

Action (90 days): Start supplier questionnaires; require firmware signing for new procurements.

10. Incident response & safety-integrated playbooks

Why: OT incidents threaten safety and environment. Build IR plans that coordinate OT engineers, safety officers, and the SOC. Include playbooks for ransomware, ICS-specific manipulation, and physical safety escalations. Practice tabletop exercises regularly. CISA and NIST recommend joint OT/IT incident drills

Action (30–60 days): Run one tabletop with operations and security teams this quarter.

11. Backup, immutable logs, and disaster recovery for control logic

Why: Back up ladder logic, HMI screens, and configuration to immutable storage. Test restoration – the goal is safe resumption of control, not just data recovery. Ensure backups are air-gapped or otherwise isolated from production networks.

Action (60–90 days): Implement automated, encrypted backups and validate restores.

12. Vendor and third-party remote support controls

Why: Third parties often require system access. Limit and log their access through jump hosts, use MFA, require least-privilege sessions, and revoke access after work. Contractually require security baselines.

Action (30 days): Enforce a vendor remote access policy and audit last 12 months’ sessions.

13. Operational resilience & safety case alignment

Why: Cybersecurity changes must not compromise safety systems. Any change must include safety impact analysis and, where necessary, regulatory notification. Align cybersecurity changes with process safety management to avoid conflicts.

Action (Ongoing): Include safety engineers in security change approvals.

14. Workforce training, simulation & ICS cyber hygiene

Why: Operators and maintenance staff are the last line of defense. Train for phishing, safe USB handling, change control, and recognizing abnormal ICS behavior. Use scenario-based drills (including OT-specific attack simulation).

Action (30–60 days): Schedule role-based training and tabletop exercises quarterly.

15. Governance, metrics and a prioritized remediation backlog

Why: A sustainable OT security program requires governance, budget, and measurable KPIs (time-to-detect, time-to-contain, patch lag, asset coverage). Use risk-based prioritization – treat controls that reduce exposure to internet-facing devices and critical safety assets as highest priority. NIST, ISA/IEC and CISA guidance all point to risk-based governance

Action (30 days): Create a 90-day prioritized remediation list and present to plant leadership.

Quick wins (30–90 days) – where plant managers get fast ROI

Disable and/or change all default passwords on controllers/HMIs.
Implement a single, audited jump host for remote access with MFA.
Build a prioritized asset inventory of top-50 critical assets.
Insert passive network taps to start monitoring traffic for anomalies.
Run one incident tabletop that includes operations, safety and IT.

These provide immediate risk reduction without heavy capital expense.

Roadmap: tactical (0–3 months), operational (3–12 months), strategic (12+ months)

0–3 months: Asset inventory, remote access controls, password changes, basic monitoring, backup verification.
3–12 months: Segmentation, device hardening, formal patch playbook, vendor controls, IR playbooks, staff training.
12+ months: Microsegmentation, zero-trust maturity steps for identity/device, SBOM adoption, supply-chain verification, mature OT/IT integration for SOC monitoring.

KPIs to track (example)

% of OT assets inventoried and classified (goal: 100%)
Mean time to detect (MTTD) OT incident (target: decrease over time)
Patch lag for critical devices (days)
Number of vendor remote sessions with auditing (100%)
Successful restore tests from OT backups (quarterly pass rate)

Common pitfalls & how to avoid them

Treating OT like IT: OT has deterministic timing and safety constraints. Test everywhere.
Over-scanning production devices: Use passive discovery and lab testing to avoid outages.
Ignoring safety integration: Always coordinate security changes with process safety teams.
One-time projects without governance: Security needs budget, owners, and metrics.

Tools & tech to consider (non-endorsement, starting points)

Passive network sensors and OT-aware IDS (for protocol awareness).
Jump hosts with session recording and MFA.
Network segmentation (physical + virtual) with strict ACLs.
Firmware integrity tools and SBOM producers.
OT asset management platforms that support passive discovery.

Quick checklist (printable)

Complete OT asset inventory (IDs, firmware, criticality)
Remove/change default accounts & harden configs
Segmentation map & enforcement in place
Controlled remote access (jump host + MFA)
Passive monitoring / baseline traffic collection
Backup and restore validation for control logic
Vendor remote access policy & audits
Patch testing environment and playbook
Incident response + tabletop with safety included
Training schedule for staff and contractors
Supplier security questionnaires / SBOM requests
Measurable KPIs and monthly reporting to plant leadership

Final thoughts – a safety-first security culture

For plant managers, OT security is not an IT checklist – it’s a continuous program that must preserve safety, reliability and availability. Start simple: inventory, remote access controls, backups and monitoring. Then grow into segmentation, hardened processes, and supply-chain assurance. Use industry standards (ISA/IEC 62443), NIST SP 800-82 Revision 3 and CISA’s recommended practices as your guardrails while tailoring implementation to the plant’s operational constraints.