Ensuring security of critical infrastructures, such as electric power systems, is an important and challenging research issue due to growing concerns for cyber attacks targeted toward these infrastructures. Traditional cyber security solutions cannot be adapted to the context of power systems due to the complex interdependency between information and power networks. In this context, our research focuses on integrated modeling of cyber-physical systems for vulnerability assessment, impact analysis, risk modeling and mitigation, and robust countermeasures, and test-bed development and validation studies.