Today, cyber threats have the potential to harm critical infrastructures which may result in the interruption of life-sustaining services, catastrophic economic damages or severe degradation of national security. The diversity and complexity of cyber threats that exploit the vulnerabilities of critical infrastructures increase every day. . In order to lessen the potential harm of cyber threats, countermeasures have to be applied and the effectiveness of these countermeasures has to be monitored continuously. In this study, a brief definition and history of critical infrastructures are introduced. Cyber threats are examined in four fundamental categories. Vulnerabilities of critical infrastructures are categorized and examined. Finally, countermeasures that may play a key role in critical infrastructure protection programs are categorized
