Which AWS service should the company use to meet these requirements?

Explanations:

Amazon GuardDuty is a managed threat detection service that continuously monitors AWS accounts and workloads for malicious activity. It provides security findings that help with visibility and remediation.

AWS Shield is a managed DDoS protection service that safeguards applications from DDoS attacks but does not focus on continuous monitoring for malicious activity across AWS accounts.

AWS WAF (Web Application Firewall) helps protect web applications from common web exploits but does not provide continuous monitoring or detailed security findings across AWS accounts.

AWS CloudTrail records AWS API calls for account activity tracking and compliance but does not actively monitor for malicious activity or provide security findings.