Best 15 Ways to Improve OT Security Without Affecting Production

The Uptime Imperative: A Background on OT Security vs. Production

In the world of Operational Technology (OT)-where physical processes are monitored and controlled by systems like SCADA, PLCs, and DCS-the core priorities are Safety and Availability (Uptime). Unlike Information Technology (IT), which prioritizes the Confidentiality of data, OT’s primary concern is ensuring the continuous, safe, and reliable operation of the plant or critical infrastructure. Every minute of unplanned downtime due to a security incident or a failed patch can cost manufacturers and utilities millions.

This fundamental difference creates a unique challenge for cybersecurity: How do you implement robust security controls without disrupting the highly sensitive, often decades-old, and real-time operational processes?

The answer lies in a strategic, layered approach that prioritizes passive, non-invasive measures and leverages the unique characteristics of the industrial network. This post outlines 15 powerful, modern strategies that allow you to dramatically enhance your OT security posture, moving from reactive defense to proactive cyber resilience, all while your plant keeps running.

Part 1: Establishing the Foundation (Strategy & Visibility)

You cannot protect what you cannot see, and you cannot secure what you do not understand. The first, and most crucial, phase of non-disruptive OT security is establishing unparalleled visibility and a clear, aligned governance structure. These steps are inherently passive and require zero operational downtime.

1. Achieve Comprehensive, Passive OT Asset Inventory and Visibility

The single most critical step in OT security is gaining a complete, accurate, and real-time inventory of every device on your network. Traditional IT scanners are dangerous in OT, as they can crash sensitive PLCs.

• The Non-Disruptive Approach: Deploy OT-specific Network Detection and Response (NDR) or Asset Discovery solutions that use passive listening (via SPAN ports or Network TAPs). These tools analyze industrial protocol traffic (like Modbus, DNP3, and Ethernet/IP) without sending any active packets to the control systems.
• High-Value Output: The result is a continuously updated database of every PLC, HMI, historian, and engineering workstation, including its vendor, model, firmware version, and communication patterns. This is the foundation for all subsequent risk reduction.

2. Map and Document Network Communications & Zoning (Purdue Model)

Once you have your asset inventory, you must understand how they communicate. A “flat” OT network-where any device can talk to any other-is a massive risk.

• The Non-Disruptive Approach: Use the passive monitoring data from Step 1 to automatically map out all communication flows. This reveals the true dependencies between systems and highlights violations of intended network architecture. Use the ISA/IEC 62443 or Purdue Enterprise Reference Architecture (PERA) models to define logical zones (e.g., Control Zone, Industrial DMZ, Business/IT Zone).
• High-Value Output: A visual, dynamic network map that clearly defines the boundaries for future segmentation. This process is purely informational and has no impact on current production.

3. Implement Continuous, Risk-Based Vulnerability Prioritization

Patching in OT is complex and risky. Most devices cannot be patched easily or without a maintenance window. Therefore, you must prioritize the vulnerabilities that pose the highest risk to operations.

• The Non-Disruptive Approach: Integrate the vulnerability data (CVEs) from your asset inventory with a risk engine that considers three factors: Vulnerability Severity (CVSS Score), Asset Criticality (e.g., a PLC is more critical than a network printer), and Threat Exposure (is the asset reachable from the IT network?).
• High-Value Output: A clear, prioritized list of the top 5-10 vulnerabilities that must be addressed, allowing you to use scarce maintenance window time most effectively. This is a risk management exercise, not an operational one.

4. Establish a Formal IT/OT Governance Steering Committee

Security is a business risk, not a technical silo. The historical wall between IT and OT must be dismantled at the leadership level.

• The Non-Disruptive Approach: Create a formal, regular meeting (a Steering Committee) jointly sponsored by the CISO (IT Security) and the VP of Operations or Plant Manager (OT/Production). This group aligns goals, prioritizes projects based on operational risk, and manages the shared budget.
• High-Value Output: A common language and shared risk register that ensures security decisions support the ultimate goal: safe, continuous production. This is purely organizational.

Part 2: Low-Impact Technical Controls (Enhancing Defenses)

These steps involve deploying new infrastructure or tools, but they are designed to be deployed out-of-band or to listen only initially, ensuring they do not interrupt the control plane.

5. Deploy OT-Specific Anomaly Detection and Threat Monitoring

Waiting for an incident to happen is no longer an option. You need to detect the subtle, early warning signs of an attack (e.g., unauthorized protocol commands, new device connections, a change in PLC logic).

• The Non-Disruptive Approach: Use the same passive NDR/Visibility solutions from Step 1. These systems baseline the “normal” behavior of the network and alert only when an anomaly occurs-such as a configuration change outside a maintenance window, or a command being sent to a PLC from a non-engineering workstation.
• High-Value Output: Real-time, contextualized alerts on suspicious activity, allowing your team to investigate without stopping the line. This is a “listen-only” defense layer.

6. Implement Secure Vendor and Remote Access Solutions

Third-party vendor access is one of the top infection vectors for OT systems. Allowing unmonitored VPN access is equivalent to giving a stranger the keys to your factory.

• The Non-Disruptive Approach: Implement a dedicated Secure Remote Access (SRA) solution with a Zero Trust architecture. This system uses a highly controlled Jump Host or Service Portal in the Industrial DMZ (IDMZ). Access is:
  • Protected by Multi-Factor Authentication (MFA).
  • Granted only for a Just-In-Time (JIT) period after a formal approval workflow.
  • Fully Monitored and Recorded (Keystrokes, screen sharing) for audit.
• High-Value Output: You gain total control and visibility over every remote connection without changing how the vendors ultimately interact with the control system-they still use their standard tools through the secure gateway.

7. Virtual Patching and Compensating Controls

Since you can’t immediately patch every vulnerability, you must introduce layers of defense around the vulnerable assets.

• The Non-Disruptive Approach: Deploy Industrial Firewalls or Intrusion Prevention Systems (IPS) logically in front of high-risk, unpatchable assets (e.g., a legacy Windows HMI). The IPS can be configured to block a specific known exploit (a virtual patch) or only allow expected, safe commands to pass, effectively shielding the device from attack without touching the device itself.
• High-Value Output: Mitigating high-severity risks without requiring the physical device to be taken offline for an update that might not even be available.

8. Enforce Strong, Non-Default Credential Management

Many OT systems ship with default, known passwords or no passwords at all. Changing these in live systems is tricky, but often manageable.

• The Non-Disruptive Approach: Begin by documenting and auditing all credentials using the passive asset inventory (Step 1). Then, target non-critical or newly installed assets first. For legacy assets, change the administrative password during scheduled maintenance, but immediately implement Multi-Factor Authentication (MFA) for all human users accessing the control network, including engineers. MFA is an application-level control that doesn’t usually impact the PLC/Controller itself.
• High-Value Output: Eliminating the easiest and most common attack vector: the exploitation of default/weak passwords.

9. Implement Application and Process Whitelisting

In OT, what is “normal” is highly predictable. PLCs run specific logic, and workstations run a limited set of applications.

• The Non-Disruptive Approach: On high-value, but non-critical, assets like Human Machine Interfaces (HMIs) and Engineering Workstations, deploy an Application Whitelisting solution. This tool observes the applications running for a period of time, creates a list of “approved” executables (the whitelist), and then prevents any other program-including malware or unauthorized tools-from ever launching. This is a very light-touch control that only restricts the launch of new software, not the ongoing process.
• High-Value Output: A massive barrier against the execution of ransomware and other malicious code, which are, by definition, unauthorized executables.

Part 3: Organizational, Procedural, and Human Controls

These strategies focus on people, processes, and documentation-areas that are completely independent of the control systems themselves but have a profound impact on overall security and resilience.

10. Develop and Test an OT-Specific Incident Response Plan

An IT-centric incident response plan is almost guaranteed to fail in an OT environment because it will prioritize data containment over safety and uptime.

• The Non-Disruptive Approach: Draft a specific OT Incident Response (IR) Playbook with the Operations team. The playbook must define clear communication protocols and prioritize: Safety first, Containment second, and Recovery third. Crucially, this involves Tabletop Exercises (TTX) and walkthroughs with the joint IT/OT teams, simulating scenarios like ransomware or a destructive malware attack.
• High-Value Output: A prepared team that can respond to a cyber event with speed, ensuring human safety and minimizing downtime, without ever touching the live system during the training.

11. Enforce an Immutable Backup and Recovery Strategy

If all else fails, your ability to recover quickly dictates your total downtime. An attacker’s goal is often to destroy backups to force a ransom payment.

• The Non-Disruptive Approach: Implement a dedicated “air-gapped” or immutable backup system for all critical PLC logic, HMI configurations, and historian data. Immutable means the data cannot be changed or deleted after it’s written. The system should disconnect from the network after the backup is complete. Regularly test the restoration process in a non-production test lab.
• High-Value Output: A guaranteed, clean recovery path that drastically reduces the time-to-safe-operating-state after a major disruption.

12. Mandatory, Context-Specific Security Awareness Training

74% of breaches involve human error, privilege misuse, or stolen credentials. Your people are your greatest asset and your greatest vulnerability.

• The Non-Disruptive Approach: Implement OT-specific security training that covers real-world industrial scenarios: recognizing phishing emails targeted at engineers, the danger of unauthorized USB drives, and the procedure for reporting a suspicious event on the plant floor.
• High-Value Output: A cyber-aware workforce that acts as the primary defense line against social engineering and unintentional errors, requiring no system modification.

13. Introduce Change Management Control and Audit

Uncontrolled changes in OT environments are a top cause of both security issues and operational failures.

• The Non-Disruptive Approach: Formalize all configuration changes (PLC code changes, firewall rule updates, new device introductions) into a strict, documented process. Use the continuous monitoring tools from Step 5 to audit all configuration changes in real-time. If a change is detected that wasn’t approved by the change management system, an immediate, high-priority alert is issued.
• High-Value Output: Enforcing discipline and immediately detecting unauthorized changes that could be benign human error or a malicious compromise.

14. Leverage Micro-Segmentation with Industrial Firewalls

Network segmentation is the most powerful defense, but it must be done with extreme care. Micro-segmentation separates small groups of assets (or even individual cells) into their own secure zones.

• The Non-Disruptive Approach: Phase 1 (Non-Disruptive): Place industrial firewalls between key zones (e.g., separating the SCADA servers from the PLCs) and configure them in a monitor/log-only mode. This allows you to collect traffic data and validate all required communication flows against your network map (Step 2) before enforcing any blocking rules. Phase 2 (Minimal Downtime): Once the rules are validated, switch the firewall to enforce mode during a pre-planned, brief maintenance window.
• High-Value Output: Limiting an attacker’s lateral movement to a tiny segment of the network, drastically reducing the blast radius of any successful breach.

15. Adopt a Framework-First Approach (IEC 62443)

Security frameworks provide a structured roadmap, preventing the “boiling the ocean” feeling that often stalls OT security programs.

• The Non-Disruptive Approach: Do not try to achieve compliance overnight. Instead, map your current and planned security controls to the relevant requirements of IEC 62443 (the global standard for ICS security). Use the framework’s structure to guide your priority list (which should align with the 14 steps above).
• High-Value Output: A globally recognized, phased plan for continuous improvement that allows you to demonstrate tangible progress to both the executive suite and regulators without requiring immediate, production-stopping changes.

Conclusion: The Path to Cyber Resilience

Improving OT security is not a project; it’s an ongoing journey of cultural and technical maturity. The key takeaway is that the most impactful security improvements-gaining visibility, controlling remote access, and preparing your team-are inherently non-disruptive and can be implemented today.

By starting with passive monitoring, governance alignment, and human factor training, you can build a resilient foundation that drastically reduces your overall risk and makes the unavoidable, production-affecting controls (like patching and segmentation enforcement) much safer and faster to implement down the line.