Research on cyber-attacks and countermeasures in interconnected critical infrastructure has gained major importance, as modern societies increasingly rely on tightly coupled systems such as power grids, water supply networks, transportation, healthcare, and communication systems. Research papers in this area focus on the vulnerabilities created by interdependencies, where a successful cyber-attack on one sector can trigger cascading failures across multiple infrastructures. Studies highlight common attack vectors such as Distributed Denial-of-Service (DDoS), ransomware, Advanced Persistent Threats (APTs), and false data injection attacks targeting supervisory control and data acquisition (SCADA) systems and industrial control systems (ICS). Countermeasure research explores intrusion detection systems, anomaly-based monitoring, resilient control mechanisms, blockchain-enabled secure communication, and artificial intelligence for predictive threat analysis. Recent works also emphasize cyber-physical resilience, risk assessment frameworks, and game-theoretic models for adversarial defense strategies. Moreover, hybrid approaches integrating federated learning, digital twins, and Zero Trust Architecture are being developed to enhance real-time monitoring and coordinated defense. Overall, the literature shows that strengthening the resilience of interconnected critical infrastructure requires not only robust technical solutions but also collaborative governance, threat intelligence sharing, and cross-sectoral preparedness.