Modbus
The lingua franca of industrial controllers; unauthenticated by design, so anything that can reach the network can command a chiller or CDU without exploiting a vulnerability.
Current numbers
>600 apartment buildings / ~2 daysFrostyGoop district-heating incident in Lviv: malicious Modbus commands; the firmware downgrade was a separate action
Port 502Classic Modbus TCP is unauthenticated, and FrostyGoop used it; Claroty finds over 80% of data-center OT on BACnet/Modbus-class protocols