"Supervisory Control And Data Acquisition (SCADA) systems, control and monitor utility infrastructure, such as electricity, gas, water etc, which happen to be part of critical infrastructure. Existing SCADA systems were originally designed for reliability. Initial SCADA systems used proprietary protocols like Modbus, DNP3 to access sensed data and initiate supervisory control. These SCADA systems were not designed with Internet security in mind, which provides challenges as these systems are migrated toward common Internet communication protocols and networks. Compared to IT systems, SCADA systems have a higher requirement concerning reliability, latency and uptime, so it is not always feasible to apply IT security measures deployed in IT systems."