PLC

What is a PLC?

A PLC (Programmable Logic Controller) is a specialised industrial computer designed to control machines and processes in manufacturing environments. It replaced traditional relay-based circuits, offering programming flexibility, resilience to industrial conditions and the ability to quickly modify control logic.

A PLC reads input signals from sensors (temperature, pressure, position), processes them according to programmed logic and generates output signals to control actuators - valves, motors, pumps. The cycle of reading, processing and writing repeats hundreds or thousands of times per second.

PLCs are present in virtually every industrial plant - from assembly lines in car factories to water treatment stations. They are programmed in languages defined by the IEC 61131-3 standard, such as Ladder Diagram and Structured Text.

Why does it matter?

PLC controllers are the point where the digital world meets the physical world. Compromising a PLC allows an attacker to directly affect a physical process - changing motor speed, opening a valve or shutting down a pump. The Stuxnet attack of 2010 demonstrated that manipulating PLC logic can lead to physical destruction of infrastructure.

Protecting PLCs requires a multi-layered approach: network segmentation, physical and logical access control, monitoring of changes to controller programmes and regular security audits. Many older controllers lack built-in authentication mechanisms, making them particularly vulnerable to attack.

Related topics

• SCADA
• DCS
• HMI
• ICS