This paper addresses scenarios and security issues when migrating SCADA systems to cloud and fog environments. Migration strategies to the cloud refer to different cloud infrastructures (public, private or hybrid) as well as selection of cloud service. Benefits of cloud-based SCADA systems mainly refer to improving economic efficiency. We further address migration risks, with regards to quality of service and cyber security. Challenges in security provisioning encompass security solutions, risk management and test environment. Finally, we address emerging evolution of SCADA toward fog computing, including the three-tier system's architecture and security issues.