Past cyber-attacks on Supervisory Control and Data Acquisition (SCADA) Systems for Critical infrastructures have left these systems compromised and caused financial and economic problems. Deliberate attacks have resulted in denial of services and physical injury to the public in certain cases. This study explores the past attacks on SCADA Systems by examining nine case studies across multiple utility sectors including transport, energy and water and sewage sector. These case studies will be further analysed according to the cyber-terrorist decision-making theories including strategic, organisational and psychological theories based on McCormick (2000). Next, this study will look into cyber-terrorist capabilities in conducting attacks according to Nelson's (1999) approach that includes simple-unstructured, advance-structured and complex-coordinated capabilities. The results of this study will form the basis of a guideline that organisations can use so that they are better prepared in identifying potential future cybersecurity attacks on their SCADA systems.