A human-machine interface (HMI) is the user interface that connects an operator to the controller for an industrial system.
Industrial control systems (ICS) are integrated hardware and software designed to monitor and control the operation of machinery and associated devices in industrial environments, including those that are designated critical infrastructure. An HMI includes electronic components for signalling and controlling automation systems.
Some HMIs also translate data from industrial control systems into human-readable visual representations of the systems. Through the HMI, an operator can see schematics of the systems and turn switches and pumps on or off, for example, or raise or lower temperatures. HMIs are usually deployed on Windows-based machines, communicating with programmable logic controllers (PLC) and other industrial controllers.
The accessibility of HMIs poses a risk for ICS security. The systems themselves have long been considered secure from malware because they were not connected to the Internet. In some cases, administrators have deliberately disabled security mechanisms.
See a brief introduction to human-machine interfaces: