10 Best Strategies to Protect Critical Infrastructure OT Assets

For decades, the Operational Technology (OT) and Industrial Control Systems (ICS) that power our critical infrastructure-from power grids and water treatment plants to manufacturing lines and oil refineries-operated under the comforting but increasingly outdated illusion of the air gap. Safety, Reliability, and Availability were the sacred trinity, with security often an afterthought.

The world has changed. The relentless push for digital transformation, the proliferation of Industrial Internet of Things (IIoT) sensors, and the full-scale IT/OT convergence have dissolved that air gap. The result is a hyper-connected, cyber-physical ecosystem where an email phishing scam in the corporate IT network can cascade into a catastrophic shutdown on the factory floor.

The modern threat landscape is no longer dominated by simple malware; it is defined by sophisticated, high-stakes adversaries: nation-state actors seeking espionage or disruption, and well-funded Ransomware-as-a-Service (RaaS) groups targeting control systems for maximum leverage. The SANS Institute 2025 survey confirms the stark truth: incidents are rising, and while detection is improving, remediation is slow, with a significant percentage of incidents taking weeks or even over a year to fully recover from. The stakes are no longer just financial; they involve public safety, environmental damage, and national security.

To achieve genuine Operational Resilience, organizations must move past check-box compliance and adopt a proactive, industrial-grade security strategy. This is not about porting IT tools to the OT network; it’s about a fundamental shift in how we approach security for systems where uptime is non-negotiable and safety is paramount.

Here are the ten best-in-class, forward-thinking strategies you must implement to protect your critical OT assets in the current and future threat landscape.

The 10 Best Strategies for Critical OT Asset Protection

1. The Foundational Imperative: Granular, Automated Asset Inventory and Risk Prioritization

You cannot protect what you don’t know exists. In complex industrial environments, an up-to-date, detailed asset inventory is the absolute cornerstone of any security program. This is more than a simple spreadsheet; it is a living, breathing map of your cyber-physical environment.

• Deep Discovery: Implement passive, agentless discovery tools that use Deep Packet Inspection (DPI) to identify every device-PLCs, RTUs, HMIs, IIoT sensors, and engineering workstations-without disrupting operations. This is crucial for legacy systems where active scanning is dangerous.
• Contextual Cataloging: Inventory must include operational context: the device’s make, model, firmware version, vendor, location, communication protocols (e.g., Modbus, OPC UA), and, most critically, its role/criticality to the physical process (e.g., Is it a Level 0 actuator or a Level 3 HMI?).
• Risk-Based Prioritization: Use the inventory data to calculate a real-time risk score. A vulnerability on a publicly-exposed HMI is a higher priority than one on an air-gapped server. This allows security teams to focus limited patching or compensating control efforts on the assets that pose the greatest risk to safety and uptime.

2. Mandatory Adoption of Zero Trust for OT/ICS

The traditional network perimeter model is dead, especially in converged IT/OT environments. Zero Trust Architecture (ZTA), which operates on the principle of “Never Trust, Always Verify,” is no longer a best practice-it is a mandatory defensive posture.

• Micro-segmentation: Break down the OT network into the smallest logical security zones (often aligning with the ISA/IEC 62443 Zones and Conduits model). This means isolating a specific production line, or even a single high-impact PLC, with a dedicated industrial firewall or data diode. A breach in one zone cannot move laterally to another.
• Strict Identity and Access Management (IAM) for Workflows: All access to OT resources must be tied to a specific identity and authenticated at every access point. Implement Multi-Factor Authentication (MFA), especially for all remote and privileged access.
• Principle of Least Privilege (PoLP): Users and applications should only have the exact permissions necessary to perform their current task-no more. For example, a maintenance technician should only be able to modify the firmware on their assigned PLC model, and only during a pre-approved maintenance window.

3. Fortifying the Convergence Point: The IT/OT DMZ

The boundary where the IT and OT networks meet-the Industrial Demilitarized Zone (IDMZ)-is the most critical junction for preventing spillover attacks. It requires a dedicated, purpose-built security architecture.

• Secure Bi-Directional Communication: Use dedicated, industrial-grade firewalls and network proxies to strictly control traffic. All communication between IT and OT should be limited to specific, necessary data flows (e.g., historians or patching servers), and the OT network should ideally only allow communication initiated from the OT side or via a secure, one-way mechanism (data diodes) for extremely sensitive environments.
• Protocol Conversion and Deep Inspection: Traditional firewalls are often blind to industrial protocols like Modbus or DNP3. Deploy Next-Generation Firewalls (NGFWs) and Intrusion Detection Systems (IDS) that can perform deep-packet inspection of OT protocols to identify malicious commands or unauthorized changes, not just IP addresses.

4. Continuous, AI-Driven Anomaly Detection and Threat Hunting

The speed and stealth of modern attacks-especially those involving nation-state actors-demand a move away from reactive, signature-based defenses.

• Behavioral Anomaly Detection: Implement specialized OT-centric Network Detection and Response (NDR) tools that establish a baseline of “normal” industrial network behavior-what devices talk to whom, what commands are typical, and what data rates are expected. Any deviation from this baseline, such as an unexpected connection attempt, a PLC configuration change, or a sudden spike in Modbus traffic, triggers an alert.
• Integrate with IT SIEM: Correlate OT alerts with enterprise security information and event management (SIEM) systems to get a unified view. This is crucial for spotting sophisticated attacks that move slowly across both IT and OT domains to establish persistence.
• Proactive Threat Hunting: Don’t wait for an alert. Use the gathered intelligence and network visibility to actively search for signs of compromise, such as unusual scheduled tasks, undocumented accounts, or remote access tunnels.

5. Secure Remote Access and Third-Party Vendor Management

Remote access-for employees, contractors, and essential third-party vendors-remains one of the highest-risk attack vectors, accounting for a significant percentage of all incidents.

• Dedicated Secure Access Platforms: Eliminate direct RDP/VNC connections. All remote access must go through a secure, industrial Privileged Access Management (PAM) or jump server solution. This allows for session recording, command logging, and real-time monitoring of all vendor activity.
• JIT (Just-in-Time) Access: Grant remote access only when explicitly requested, approved by an internal OT manager, and automatically revoked after a set, short period of time. This minimizes the window of opportunity for an attacker.
• Strictly Enforced MFA: Require MFA for all remote access logins, ensuring that compromised credentials alone are insufficient for breach.

6. The Hard Problem: A New Approach to Patching and Vulnerability Management

Due to long system lifecycles, vendor warranties, and the zero-downtime mandate, traditional IT patching cycles are impossible in OT. A new, risk-based approach is required.

• Compensating Controls and Virtual Patching: For systems that cannot be patched immediately (or ever), prioritize compensating controls. This could involve segmenting the vulnerable device into a highly isolated zone, deploying a dedicated protocol filter, or using virtual patching technologies on a security appliance to block known exploit traffic before it reaches the vulnerable asset.
• Risk-Based Remediation: Focus on vulnerabilities that are remotely exploitable or affect critical safety systems first. Use a structured, documented process to plan, test, and implement patches during scheduled downtime, often aligning with process restarts.

7. Cyber-Informed Engineering and Secure-by-Design Principles

The most effective defense is building security in from the start, not bolting it on later. This is a crucial shift toward Cyber-Informed Engineering (CIE).

• System Hardening: Implement secure configuration baselines. Disable unnecessary ports and services on controllers, HMI workstations, and servers. Change all default passwords immediately.
• Application Whitelisting (Allowlisting): On critical workstations and servers, only permit authorized applications and files to execute. This is far more effective than traditional blacklisting (antivirus) against advanced, unknown malware strains.
• Secure Development Lifecycle (SDL): Demand that system integrators and vendors follow a secure development process, providing evidence of secure coding practices and vulnerability testing before deployment.

8. Incident Response and Recovery Planning with an OT Focus

An incident is not a possibility-it’s a certainty. The true measure of resilience is not whether you are attacked, but how quickly and effectively you can recover without compromising safety.

• OT-Specific IR Plan: Develop an Incident Response (IR) plan distinct from the IT plan. It must prioritize safety and operational continuity over digital forensics. The first steps in an OT incident are physical, often involving emergency shutdowns or failover procedures.
• Air-Gapped, Tested Backups: Maintain frequent, verifiable, and physically or logically air-gapped backups of all critical PLC/controller logic, HMI configurations, and historical data. Crucially, these backups must be regularly tested to ensure they can be restored without issue.
• Drills and Tabletop Exercises: Run frequent, realistic tabletop exercises with both IT and OT staff, simulating scenarios like a ransomware attack on the engineering workstation or a remote attacker manipulating a critical valve. This bridges the IT/OT cultural gap under pressure.

9. Operationalizing the Human Element: Training and Culture

In the high-stakes environment of critical infrastructure, the human element remains the most significant variable, whether through error or targeted social engineering.

• Role-Specific Training: Move beyond generic training. Provide tailored cybersecurity education for different roles:
  • Operators: Train them to recognize unusual control panel behavior or physical tampering.
  • Engineers: Train them on secure coding, change management, and safe remote connection procedures.
  • Management: Train them on the critical differences between IT and OT risk and the financial/reputational consequences of a breach.
• Fostering a Culture of Security: Create an environment where employees are encouraged, not punished, to report suspicious activity, whether it’s a strange email or an unknown USB drive. Empowering the front line is your most cost-effective defense.

10. Proactive Regulatory Adherence and Intelligence Sharing

As governments globally recognize the threat to critical infrastructure, regulations are intensifying (e.g., NERC CIP, NIS2, stricter CISA guidance). Staying ahead of compliance provides a structure for superior security.

• Align with Standards: Use globally recognized standards like ISA/IEC 62443 and the NIST Cybersecurity Framework (CSF) as the bedrock for your OT security program, as these are the models regulators are increasingly adopting.
• Threat Intelligence Collaboration: Actively engage with Information Sharing and Analysis Centers (ISACs) relevant to your sector (e.g., Electricity ISAC, WaterISAC). Sharing and receiving timely, verified threat intelligence on new ICS-specific malware, zero-day exploits, or targeted campaigns is vital for pre-emptive defense. This intelligence should be fed directly into your anomaly detection and firewall rules.

The Path to True Operational Resilience

The era of reactive, perimeter-based security in critical infrastructure is over. Protecting modern OT assets requires a holistic, operational-first strategy that acknowledges the convergence of the digital and physical worlds.

By implementing these ten advanced strategies-moving from static asset lists to a living, contextual inventory, adopting a Zero Trust mindset, leveraging AI for anomaly detection, and building security into the engineering lifecycle-organizations can elevate their security posture from mere compliance to genuine Operational Resilience. This shift is not just an IT project; it is a business imperative that safeguards the vital services that underpin our society.