PLC
Programmable Logic Controller
Speicherprogrammierbare Steuerung (SPS)
A PLC is a robust industrial computer that directly controls a physical process — it reads sensors and switches actuators according to a stored logic. PLCs are the workhorses of automation and are found in almost every facility. Whoever controls a PLC controls the process.
History & facts. PLCs are built for reliability and long service life, not for cybersecurity: many possess no integrity check of their programming and trust commands that arrive over the network. This is exactly where formative attacks took hold — Stuxnet manipulated the programming of Siemens PLCs, PIPEDREAM targeted widespread PLCs of various manufacturers generically. The direct relationship to the physical process makes the PLC the most critical element of OT.
Outlook & recommendation. Since PLCs often cannot be readily hardened or patched, protection lies in the surroundings: strict segmentation, control of the engineering access (via which PLCs are programmed) and monitoring for unexpected program or command changes. Changes to the PLC logic are to be treated as highly critical events. Securing this level is the core of any serious OT security strategy.