OT Security Engineer Interview Questions UK: 8 Real Questions and What Interviewers Want

Applying for a OT Security Engineer job in the UK? Here is what you are likely to be asked. These questions come from our OT Security Engineer question bank of 12 questions, written for UK employers at mid-level level.

Eight OT Security Engineer interview questions, and what the interviewer is thinking

1. How does the Purdue model help you design and secure an industrial network, and where do you put the DMZ?

Why they ask: They want to see you can apply the standard architecture reference for OT networks.

2. Why can't you patch an OT environment the way you would a corporate network, and what do you do instead?

Why they ask: They want to know you understand availability and safety constraints in OT.

3. What is IEC 62443 and how have you used it?

Why they ask: They want evidence you can work with the main OT security standard series.

4. How would you gain visibility of an OT network without disrupting live processes?

Why they ask: They want to test your knowledge of safe monitoring approaches and tooling.

5. How would you secure remote access for third-party vendors who support the plant?

Why they ask: Vendor remote access is a classic OT attack path and they want a layered answer.

6. Your monitoring tool alerts that an engineering workstation has sent a new firmware download command to a PLC outside any change window. What do you do?

Why they ask: They want to see calm, safe incident handling that involves operations.

7. Tell me about a time you worked with control or process engineers to introduce a security change into a live operational environment.

Why they ask: They want evidence you can collaborate with engineers who may distrust IT security.

8. What attracted you to OT security rather than IT security, and what makes a good OT security engineer?

Why they ask: They want to gauge genuine interest and understanding of the role's distinct demands.

A sample answer to question 1

How does the Purdue model help you design and secure an industrial network, and where do you put the DMZ?

The Purdue model splits an industrial environment into levels: Level 0 and 1 are sensors, actuators and PLCs, Level 2 is local supervisory control such as HMIs, Level 3 is site operations, then the IT zones above, with a demilitarised zone between them. I use it to decide where traffic is allowed to flow and to stop direct IT to control-network connections. The industrial DMZ, usually at Level 3.5, hosts anything that needs to cross the boundary, such as historians, patch servers, jump hosts and remote access gateways, so no session is ever terminated straight onto a PLC. Firewalls enforce explicit allow-lists by protocol and port, for example Modbus TCP or OPC UA, and I align the zones and conduits with IEC 62443-3-2. I accept the model is a guide rather than gospel, because cloud analytics and IIoT blur the layers, so I document exceptions and compensate with monitoring and tighter rules.

Common mistake to avoid: Reciting levels without explaining enforcement; Treating the model as an IT network diagram

Want the rest?

Full model answers, key points and common mistakes for all 12 questions are on the OT Security Engineer interview questions page. The first five are free, no sign-up needed.