Amazon GuardDuty is the correct answer because it is specifically designed as a threat detection service that continuously monitors for malicious or unauthorized activities. Amazon GuardDuty applies machine learning and anomaly detection to identify unexpected and potentially unauthorized or malicious activity within your cloud environment. AWS Security Hub provides a comprehensive view of security alerts and security posture across your accounts. Amazon Inspector is focused on the security assessment of applications running on the cloud, whereas AWS Shield specifically provides protection against DDoS attacks.