Today, this belief is not just outdated; it’s dangerous.

As a cybersecurity leader specializing in OT, I can tell you that the air gap is a myth. Relying on it is the equivalent of a castle guard believing the walls are impenetrable, all while the enemy is tunneling underneath.

The reality is your air gap is, at best, a speedbump. It’s full of holes you can’t see, and it’s distracting you from the real work: securing the network inside the walls.

How the “Air Gap” Is Breached Every Day

An air gap is only as strong as its weakest link, and those links are everywhere. The breach doesn’t happen with a sophisticated hack; it happens through routine, everyday operations.

1. The Infected USB Drive A vendor or technician arrives on-site to update a PLC. They plug in a USB drive that they also used on their home computer, which was infected with malware. The malware now jumps the “gap” and is inside your most sensitive network. This isn’t a theory; this is how the infamous Stuxnet worm operated.

2. The “Accidental” Bridge An engineer needs to troubleshoot a machine from their office. They set up a “temporary” (and forgotten) wireless access point on the OT network so they don’t have to walk down to the plant floor. Your air gap is now broadcasting to the parking lot.

3. The “Shadow IIoT” Device You just installed a new, state-of-the-art compressor. You don’t know it, but the vendor built in a “hidden” 4G modem so they can remotely monitor its performance. Your network is now connected to the cellular network, and you have no idea.

4. The “Strategic” Bridge (That Nobody Secured) This is the most common vulnerability I see. The business needs production data for its new IT platform, so you build a connection. As I discussed in my previous article on [Link to your “IT Modernization” post]the risks of IT/OT modernization[/Link], that new, data-driven connection is a permanent, six-lane superhighway built straight through your non-existent “gap.”

The Problem: A Flat, Fragile Interior

Breaching the air gap is the easy part. The real danger is what happens next.

Because you believed the air gap was working, you probably invested nothing in internal security. Once an attacker is “inside,” they are on a flat, wide-open network. They can move from machine to machine with zero resistance, mapping your entire operation, stealing data, or preparing to shut you down.

Relying on an air gap is a “hard shell, soft center” strategy. And the shell is already broken.

The Solution: Move From “Air Gap” to “Assume Breach”

The modern, defensible strategy is to assume your perimeter will be breached. Security is no longer about building a perfect wall; it’s about building internal walls that contain an intruder.

1. Gain Full Visibility You cannot protect what you cannot see. The first step is to deploy passive monitoring tools built for OT networks. These tools listen to network traffic without disrupting operations, giving you a complete map of every asset, connection, and vulnerability on your network.

2. Implement Network Segmentation This is the single most effective “fix.” Stop thinking about one “air gap” and start thinking in “zones.” Based on frameworks like the [Link to your “Industrial Standards” category]NIST and ISA/IEC 62443 standards[/Link], you must segment your network into logical zones with firewalls between them. A breach in “Zone 1” (e.g., secondary controls) is contained and cannot spread to “Zone 0” (your most critical PLCs).

3. Build a Secure “Bridge” (The IDMZ) Acknowledge that you need data to flow between IT and OT. Stop pretending you can keep them separate. The solution is to build a purpose-built, secure “bridge” known as an Industrial Demilitarized Zone (IDMZ). All traffic is forced through this single, heavily-monitored checkpoint, allowing you to get business data out without letting attacks in.

Your air gap is a comforting lie. The reality is that true OT security is an ongoing, active process of monitoring, segmenting, and managing risk.