- A
Apply a new security group that denies all inbound and outbound traffic to the instance.
This instantly isolates the instance from the network, stopping the C2 traffic while preserving the instance for forensic investigation.
- B
Remove the security group from the Auto Scaling group to isolate the instance.
Why wrong: Removing the security group from the Auto Scaling group would affect all instances and does not specifically isolate the compromised instance.
- C
Terminate the EC2 instance immediately to stop the communication.
Why wrong: Terminating destroys the instance and any volatile data needed for forensic analysis.
- D
Create an AMI of the instance for forensic analysis and then terminate the instance.
Why wrong: Creating an AMI does not stop the ongoing C2 communication; the threat continues during AMI creation.
SCS-C02 Threat Detection and Incident Response Practice Question
This SCS-C02 practice question tests your understanding of threat detection and incident response. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. 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 company runs a web application on an Auto Scaling group of EC2 instances behind an Application Load Balancer. The application stores user session data in an ElastiCache Redis cluster. The security team receives an alert from GuardDuty that one of the EC2 instances is communicating with a known command-and-control (C2) IP address. The instance ID is i-0a1b2c3d4e5f. The security engineer needs to contain the threat immediately while preserving the instance for forensic analysis. Which course of action should the security engineer take?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue:
"immediately / without restart"Why it matters: Time or reboot constraint — the correct answer must take effect right away without requiring a reboot or reload.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
Apply a new security group that denies all inbound and outbound traffic to the instance.
Option A is correct because applying a new security group that denies all inbound and outbound traffic immediately stops the C2 communication at the network layer without destroying the instance. This preserves the instance for forensic analysis (e.g., memory dump, disk imaging) while containing the threat. The security group acts as a virtual firewall, and changing it is a non-destructive, reversible action that can be applied directly to the instance even if it is part of an Auto Scaling group.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
Apply a new security group that denies all inbound and outbound traffic to the instance.
Why this is correct
This instantly isolates the instance from the network, stopping the C2 traffic while preserving the instance for forensic investigation.
Clue confirmation
The clue word "immediately / without restart" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
Remove the security group from the Auto Scaling group to isolate the instance.
Why it's wrong here
Removing the security group from the Auto Scaling group would affect all instances and does not specifically isolate the compromised instance.
- ✗
Terminate the EC2 instance immediately to stop the communication.
Why it's wrong here
Terminating destroys the instance and any volatile data needed for forensic analysis.
- ✗
Create an AMI of the instance for forensic analysis and then terminate the instance.
Why it's wrong here
Creating an AMI does not stop the ongoing C2 communication; the threat continues during AMI creation.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often choose to terminate the instance (Option C) thinking it is the fastest containment, but they overlook the critical requirement to preserve the instance for forensic analysis, which termination destroys.
Detailed technical explanation
How to think about this question
Under the hood, security groups are stateful and evaluated at the instance level; applying a new group with deny-all rules (e.g., no inbound or outbound rules) effectively drops all traffic at the hypervisor level before it reaches the instance. In a real-world scenario, the security engineer should also consider taking a forensic snapshot of the EBS volume and capturing memory using tools like LiME or F-Response before any network isolation to preserve evidence. The GuardDuty finding would include the specific C2 IP and port, which can be used to create a targeted deny rule, but immediate blanket isolation is the fastest containment step.
KKey Concepts to Remember
- Read the scenario before looking for a memorised answer.
- Find the constraint that changes the correct option.
- Eliminate answers that are true in general but not in this case.
TExam Day Tips
- Watch for words such as best, first, most likely and least administrative effort.
- Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
How this comes up in practice
A healthcare organisation deploys an application with a public-facing web tier and a private database tier. The database subnet has no public IP and only accepts connections from the web tier's security group. Questions like this test whether you can design cloud network isolation using VNets/VPCs, subnets, and security group rules.
What to study next
Got this wrong? Here's your next step.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
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FAQ
Questions learners often ask
What does this SCS-C02 question test?
Threat Detection and Incident Response — This question tests Threat Detection and Incident Response — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Apply a new security group that denies all inbound and outbound traffic to the instance. — Option A is correct because applying a new security group that denies all inbound and outbound traffic immediately stops the C2 communication at the network layer without destroying the instance. This preserves the instance for forensic analysis (e.g., memory dump, disk imaging) while containing the threat. The security group acts as a virtual firewall, and changing it is a non-destructive, reversible action that can be applied directly to the instance even if it is part of an Auto Scaling group.
What should I do if I get this SCS-C02 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Are there clue words in this question I should notice?
Yes — watch for: "immediately / without restart". Time or reboot constraint — the correct answer must take effect right away without requiring a reboot or reload.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Last reviewed: Jun 24, 2026
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