Which AWS service provides threat detection by monitoring for malicious activities and unauthorized actions to protect AWS accounts, workloads, and data that is stored in Amazon S3?

Explanations:

AWS Shield is a managed DDoS protection service that safeguards applications running on AWS. It does not focus on threat detection for malicious activities or unauthorized actions.

AWS Firewall Manager is a security management service that allows users to centrally configure and manage firewall rules across their accounts. It is not primarily designed for threat detection in the same way that GuardDuty is.

Amazon GuardDuty is a threat detection service that continuously monitors AWS accounts, workloads, and data stored in Amazon S3 for malicious activities and unauthorized actions. It uses machine learning and threat intelligence to identify potential threats.

Amazon Inspector is a security assessment service that helps improve the security and compliance of applications deployed on AWS. It assesses applications for vulnerabilities but does not focus on ongoing threat detection like GuardDuty.