Legacy industrial control systems, including programmable logic controllers and sensors, were engineered for isolated environments without built-in authentication, encryption, or intrusion detection. When connected to modern networks, these devices create an expanded attack surface that determined adversaries can exploit. Bridging this security gap is now a top-tier cybersecurity priority for manufacturing, energy, and critical infrastructure operators.
When these legacy systems are exposed to modern networks without proper safeguards, they create an expanded attack surface — one that determined adversaries can exploit. Bridging the gap between decades-old technology and today’s connectivity standards is not straightforward, but it is fast becoming a top-tier cybersecurity priority.
Why Are Legacy OT Systems a Cybersecurity Risk?
Legacy industrial control systems, programmable logic controllers, and sensors predate IP-based networking. They were built for closed, isolated environments, with no built-in authentication, encryption, or intrusion detection. Once connected to enterprise networks or the internet, these devices can unintentionally provide entry points for attackers who intercept unencrypted protocols or exploit default credentials that were never changed after installation.
What Are the Most Common OT Security Mistakes?
Organizations routinely underestimate the complexity of securing legacy operational technology environments. The most frequent mistakes share a common pattern: security was not part of the original design, and retrofitting it is treated as a low priority. The result is a set of known, preventable vulnerabilities that attackers actively target in industrial settings across manufacturing, energy, and critical infrastructure.
How Do You Secure Legacy Systems with Defense-in-Depth?
A layered, defense-in-depth strategy offers the strongest protection for legacy industrial environments. Security controls must be applied at every stage of the data path, from the device itself through to cloud applications. According to Andrew Foster, Product Director at IOTech, this means combining protocol translation, certificate-based authentication, continuous edge monitoring, and strong OT/IT network segmentation into a single coordinated framework.
A new generation of Edge computing platforms can play a pivotal role here. By securely interfacing with older equipment, performing local processing, and enforcing security policies at the edge, they can help organizations modernize without exposing themselves to unnecessary risk.
Both commercial and open-source, industrial grade, edge platform implementations have emerged over the last few years and have reached a level of maturity where they are being used successfully in large scale production deployments.
For example, a key open-source initiative with broad cross-industry support is the Linux Foundation’s LF Edge. The objective of LF Edge is to establish an open, interoperable framework for edge computing. EdgeX Foundry is one of the largest projects under the LF Edge umbrella. It provides a flexible and scalable open software platform that facilitates secure interoperability between OT devices, applications at the edge and IT/Cloud services.
How Do You Scale OT Security Across Multiple Sites?
Protecting one facility is challenging; extending that protection across dozens or hundreds of industrial sites requires a fundamentally different approach. Centralized orchestration of security updates, configuration changes, and access policies is essential, as is consistent enforcement of best practices at every location. Forward-looking operators are aligning with IEC 62443, the international standard that provides a framework for securing industrial automation and control systems.
What Are the Next Steps for IIoT Security?
The industrial sector’s digital transformation depends on connecting systems that were never intended to be connected. The benefits are substantial, but so are the risks. With careful planning, modern edge computing platforms, and a layered security approach, organizations can integrate legacy systems into IIoT architectures without sacrificing safety or reliability. Treating security as an afterthought invites avoidable vulnerabilities that can undermine the entire initiative.
About the author
This article was written by Andrew Foster. He is Product Director at IOTech, with over 20 years of experience developing IoT and Distributed Real-time and Embedded (DRE) software products. He has held senior roles in Product Delivery, Management, and Marketing, and frequently speaks at industry conferences on distributed computing, middleware, embedded technologies, and IoT. Andrew holds an M.S. in Computer-Based Plant and Process Control and a B.Eng. in Digital Systems.
Related Reading
OT Cybersecurity for Manufacturers: 2026 Guide
