Amazon GuardDutyis a threat detection service that continuously monitors AWS accounts and workloads for malicious activity and unauthorized behavior to help protect your AWS resources. It uses machine learning, anomaly detection, and integrated threat intelligence to detect when an instance or account might be compromised or if there are threats from attacks.

B. AWS WAF: Incorrect, as it is a web application firewall that protects against common web exploits but does not provide comprehensive threat detection.

C. AWS Shield: Incorrect, as it provides protection against DDoS attacks but does not detect compromises within AWS accounts.

D. Amazon Inspector: Incorrect, as it is a service that helps improve the security and compliance of applications deployed on AWS by assessing for vulnerabilities, not for threat detection.

AWS Cloud References:

Amazon GuardDuty