PLCs, connected to monitoring stations via a facility’s production network, were in a constant state of chatter with the machines, sending frequent status reports and updates to give operators a real-time view of whatever equipment and operations the PLC controlled. The Siemens .DLL was central to both the Step 7 and WinCC programs, serving as middleman to create commands for the PLCs or receive status reports from them. That’s where Stuxnet’s rogue .DLL came in. It did everything the real .DLL was designed to do, and more.
