Why legacy systems need a modern OT security strategy

Operational technology (OT) forms the backbone of industries like manufacturing, energy, and critical infrastructure.  These systems, once isolated and secure, are now increasingly connected due to digitalisation and IT/OT integration. This shift unlocks new efficiencies but also introduces cyber risks that could disrupt production, compromise safety, and damage sensitive data. With evolving threats and regulatory frameworks like NIS2, organisations need tailored security strategies to stay resilient.

Why OT security is different

Unlike IT networks, OT environments are built for operational continuity, not frequent software updates or quick replacements. Many industrial systems have long life cycles, often running for 20 years or more. The challenge is that much of this legacy infrastructure depends on outdated or end-of-life (EOL) software, such as Windows XP or Windows 7, which no longer receive security patches.

These environments are further complicated by flat networks that connect all devices directly to a core switch, creating an environment where a single cyber threat can propagate rapidly. Additionally, air-gapped networks and remote sites often lack consistent internet connectivity, making it hard to patch or monitor systems. As organisations attempt to modernise, they also face human factors—whether it’s misconfigurations or accidental errors by operators or third-party contractors, vulnerabilities can emerge without warning.

The cost of cybersecurity gaps

The risks tied to insecure OT environments can be devastating. Production downtime is one of the most immediate and visible effects. In industries like manufacturing, even a brief halt in operations can result in millions of dollars in losses.

Legacy systems that are difficult to protect can also drive up capital expenses. If organisations fail to secure ageing infrastructure, they may be forced to prematurely replace it, increasing operational costs. Beyond financial implications, data breaches are a growing concern. Modern OT environments transmit operational data to IT systems for performance analysis, creating an avenue for attackers to compromise both OT and enterprise networks. With compliance standards like NIS2 becoming stricter, failure to secure these assets could result in fines, legal action, and reputational damage.

A multi-layered security approach to protecting OT

Effective OT cybersecurity strategies don’t rely on a single tool or method. Instead, a multi-layered approach ensures that all aspects of the network—legacy devices, modern equipment, and human operators—are protected.

Network segmentation:

One of the most crucial components of any OT security strategy is isolating critical systems from non-critical ones. This prevents cyber threats from spreading unchecked and limits the damage if an asset is compromised. Proper segmentation creates isolated zones within the network, protecting sensitive machinery from external connections and lateral attacks.

Tailored endpoint protection:

Legacy systems often can’t accommodate traditional antivirus or endpoint detection software due to performance constraints or incompatibility. Instead, non-intrusive security solutions can be used to monitor these endpoints externally, identifying and mitigating threats without interrupting operations.

Proactive threat detection:

Relying solely on reactive responses to cyberattacks is no longer sufficient. Proactive threat detection involves continuously monitoring devices, network traffic, and system behaviour to catch anomalies early. OT-specific security tools can provide real-time insights into potential threats, ensuring quicker response times and better protection.

Zero Trust architecture

Unlike traditional models, zero trust does not assume that anything within the network is automatically safe. Every access attempt, device, or data flow is verified, and access is only granted based on strict verification rules. This approach is essential for environments where both legacy and modern devices coexist, as it minimises exposure to internal and external threats.

Managing mixed OT environments

A global manufacturing company once attempted to apply traditional IT security practices to its OT network. Their solution, which focused on installing endpoint protection software across all devices, failed when it encountered legacy machines that couldn’t handle the updates.

As a result, production was disrupted, and the company incurred losses. This experience highlights the importance of selecting OT-specific solutions that align with operational needs, particularly in mixed environments where older machines still play a critical role.

Securing digitalisation and operational continuity

With digitalisation driving growth, organisations can’t afford to leave their OT assets vulnerable. Cybersecurity in OT is more than risk mitigation—it’s about enabling secure innovation and long-term efficiency. By adopting a multi-layered approach, organisations can:

• Extend the lifespan of legacy assets, protecting their initial investments and reducing costly replacements
• Ensure seamless and secure IT/OT integration without sacrificing productivity
• Maintain compliance with regulatory standards like NIS2, reducing legal risks

In the end, OT cybersecurity isn’t just a defensive measure—it’s a strategic asset that protects operations and fuels future growth. With the right approach, businesses can embrace digitalisation without compromising safety or reliability.

Collaborating for stronger OT security

To help organisations navigate the growing complexity of industrial cybersecurity, Nomios works with trusted partners who offer proven, OT-native solutions. One such partner is TXOne Networks, whose technology complements our approach to building secure and resilient OT environments.

Why Nomios partners with TXOne Networks

TXOne Networks focuses on practical cybersecurity for OT environments, helping industries maintain system availability and operational safety through zero-trust principles. Their solutions are designed to work with the realities of industrial operations, including legacy equipment and complex network setups.

Nomios works closely with TXOne to support organisations in improving their OT security posture. Our engineers understand the demands of industrial environments and can help integrate TXOne’s tools in a way that supports daily operations without adding unnecessary complexity.