Quick Answer
Amazon GuardDuty is the correct choice because it is purpose-built to detect suspicious API calls and other anomalous activity across your AWS environment. It continuously analyzes AWS CloudTrail management and data events, VPC Flow Logs, and DNS logs using machine learning and anomaly detection, making it ideal for identifying patterns like an IAM role on an EC2 instance making a high volume of requests to an S3 bucket outside your account—a classic sign of compromised credentials or data exfiltration. On the AWS Certified Security Specialty SCS-C02 exam, this question tests your understanding of GuardDuty’s core capability to monitor API call behavior, not just network traffic or resource configurations. A common trap is confusing GuardDuty with Amazon Inspector (which scans for vulnerabilities) or AWS Config (which tracks resource compliance). Remember the memory tip: GuardDuty is your “guard” for duty logs—if it involves unusual API calls, think GuardDuty first.
This SCS-C02 practice question tests your understanding of threat detection and incident response. Match the stated requirement to the specific cloud service, access model, or configuration option — many options are valid in isolation but not for this scenario. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
A security engineer notices that an IAM role used by an EC2 instance is generating a large number of API calls to an S3 bucket that is not part of the company's account. Which AWS service should be used to detect and alert on this suspicious activity?
AWS CloudTrail
Why wrong: CloudTrail logs API calls but does not detect suspicious patterns by itself.
Amazon Inspector
Why wrong: Amazon Inspector assesses EC2 vulnerabilities, not API behavior.
AWS Config
Why wrong: AWS Config evaluates resource compliance, not anomaly detection.
Amazon GuardDuty
GuardDuty uses machine learning to detect unusual API activity across accounts.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
Amazon GuardDuty
Amazon GuardDuty is the correct service because it uses machine learning and anomaly detection to analyze AWS CloudTrail management and data events, VPC Flow Logs, and DNS logs. It can detect unusual API calls, such as an EC2 instance role making a high volume of requests to an S3 bucket outside the company's account, which is a classic indicator of compromised credentials or data exfiltration. GuardDuty generates findings and can integrate with Amazon CloudWatch Events to trigger alerts or automated remediation.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
For each option: why learners choose it and why it is or isn't the right answer here.
AWS CloudTrail
Why it's wrong here
CloudTrail logs API calls but does not detect suspicious patterns by itself.
Amazon Inspector
Why it's wrong here
Amazon Inspector assesses EC2 vulnerabilities, not API behavior.
AWS Config
Why it's wrong here
AWS Config evaluates resource compliance, not anomaly detection.
Amazon GuardDuty
Why this is correct
GuardDuty uses machine learning to detect unusual API activity across accounts.
Related concept
Read the scenario before looking for a memorised answer.
Common exam traps
The trap here is that candidates often confuse CloudTrail (which logs the activity) with GuardDuty (which analyzes and alerts on the activity), leading them to select CloudTrail because they think logging alone is sufficient for detection, but GuardDuty is the service specifically designed for threat detection and alerting.
Detailed technical explanation
GuardDuty uses integrated threat intelligence feeds (e.g., from CrowdStrike, Proofpoint) and machine learning models to baseline normal account behavior. When it detects an IAM role making a high volume of S3 GetObject or PutObject calls to an external bucket, it generates a finding like 'UnauthorizedAccess:IAMUser/InstanceCredentialExfiltration' or 'Backdoor:EC2/C&CActivity.B'. This finding includes details such as the source IP, user agent, and the specific API calls, enabling security teams to investigate and respond quickly.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
A media company stores terabytes of video archives that are accessed once a year for audit purposes. Moving these objects to a cold storage tier (Azure Archive, S3 Glacier, or Google Nearline) costs a fraction of hot storage. Questions like this test whether you understand storage tiers, access frequency tradeoffs, and retrieval latency requirements.
What to study next
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FAQ
Threat Detection and Incident Response — This question tests Threat Detection and Incident Response — Read the scenario before looking for a memorised answer..
The correct answer is: Amazon GuardDuty — Amazon GuardDuty is the correct service because it uses machine learning and anomaly detection to analyze AWS CloudTrail management and data events, VPC Flow Logs, and DNS logs. It can detect unusual API calls, such as an EC2 instance role making a high volume of requests to an S3 bucket outside the company's account, which is a classic indicator of compromised credentials or data exfiltration. GuardDuty generates findings and can integrate with Amazon CloudWatch Events to trigger alerts or automated remediation.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Read the scenario before looking for a memorised answer.
About these practice questions
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Same concept, more angles
These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
Variation 1. A security engineer needs to detect and respond to malware on an EC2 instance. Which TWO AWS services can be used together to achieve this? (Choose TWO.)
easyWhy B: AWS Lambda is correct because it can be used as a serverless compute target to automate incident response actions when malware is detected. For example, a Lambda function can be triggered by a GuardDuty finding to isolate the compromised EC2 instance by modifying security group rules or detaching the instance from an Auto Scaling group, enabling rapid, automated remediation without manual intervention.
Last reviewed: Jun 24, 2026
This SCS-C02 practice question is part of Courseiva's free Amazon Web Services certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the SCS-C02 exam.
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