Abstract—SCADA (Supervisory Control and Data Acquisition) refers to the combination of telemetry and data acquisition [1]. Modern public infrastructure systems use SCADA systems for daily operation. This includes water treatment systems; electric power transmission, distribution, and generation; petroleum storage and refineries; chemical production and processing; railroads and mass transit; and manufacturing. The SCADA system provides monitoring, data analysis, and control of the equipment used to manage most public infrastructure systems. Little attention was given to security considerations in the initial design and deployment of these systems, which has caused an urgent need to upgrade existing systems to withstand unauthorized intrusions potentially leading to terrorist attacks. The security of these systems is critical for the operation of our society. Security of these services should have high priority. This paper identifies threats faced by SCADA and investigates effective methods to enhance its security by analyzing DNP3 protocols, which has become a de facto industry standard protocol for implementing the SCADA communications. Finally we will summarize our results and try to recommend methods to overcome the vulnerabilities on these systems.