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Application & OT Security · Foundational

Programmable Logic Controller (PLC)

A ruggedized industrial computer that reads inputs from sensors and controls outputs to machinery according to a stored program.

Definition

PLCs execute ladder logic or other IEC 61131-3 languages in deterministic scan cycles. Many accept program changes over the network with little or no authentication, so they must be protected by segmentation, key switches or run modes and change monitoring. Stuxnet targeted Siemens PLCs.

Example

A PLC opens a valve when a tank level sensor exceeds a set point.

Exam tip

PLC logic changes are a high-impact attack; monitor and restrict engineering access.

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