Quick Answer
The answer is to remove the instance from the target group and apply a security group that denies all traffic. This approach immediately stops exfiltration by cutting off new connections from the Application Load Balancer and halting any ongoing outbound traffic, all while preserving the EC2 instance and its attached EBS volumes for forensic analysis. On the AWS Certified Security Specialty SCS-C02 exam, this scenario tests your understanding of incident response containment strategies that prioritize evidence preservation over brute-force actions like termination or shutdown, which would destroy volatile memory and logs. A common trap is choosing to detach the instance or modify the Auto Scaling group, but those actions either lose data or fail to stop traffic instantly. Memory tip: think “isolate, don’t obliterate”—the goal is to quarantine the instance without deleting it, keeping the disk and memory intact for later investigation.
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 security engineer notices that an EC2 instance is sending outbound traffic to a known malicious IP address. The instance is part of an Auto Scaling group behind an Application Load Balancer. The engineer needs to immediately stop the exfiltration while preserving forensic evidence. What is the BEST course of action?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "best"
Why it matters: Signals that multiple options may be partially correct. Choose the option that most directly solves the exact problem described, not the one that sounds most complete.
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.
Detach the EBS volume from the instance.
Why wrong: Does not stop network traffic.
Terminate the EC2 instance immediately.
Why wrong: Terminating destroys evidence.
Shut down the instance from within the OS.
Why wrong: May lose volatile data and does not isolate network immediately.
Remove the instance from the target group and apply a security group that denies all traffic.
Stops traffic and preserves the instance for investigation.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
Remove the instance from the target group and apply a security group that denies all traffic.
Option D is correct because removing the instance from the target group immediately stops new traffic from the Application Load Balancer to the instance, while applying a security group that denies all outbound traffic (e.g., a custom security group with no outbound rules) halts any ongoing exfiltration without destroying the instance or its attached EBS volumes. This preserves the forensic evidence (memory, disk, logs) for later analysis, unlike termination or shutdown which could lose volatile data.
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.
Detach the EBS volume from the instance.
Why it's wrong here
Does not stop network traffic.
Terminate the EC2 instance immediately.
Why it's wrong here
Terminating destroys evidence.
Shut down the instance from within the OS.
Why it's wrong here
May lose volatile data and does not isolate network immediately.
Remove the instance from the target group and apply a security group that denies all traffic.
Why this is correct
Stops traffic and preserves the instance for investigation.
Clue confirmation
The clue words "best", "immediately / without restart" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
Common exam traps
The trap here is that candidates often choose 'Terminate the EC2 instance immediately' (Option B) thinking it stops the exfiltration fastest, but they overlook the need to preserve forensic evidence and the fact that termination destroys the instance and its associated data, making post-incident analysis impossible.
Detailed technical explanation
When an instance is removed from the target group, the ALB stops routing new requests to it, but existing connections may persist until they time out; applying a security group with a deny-all outbound rule (e.g., an empty outbound rule set) immediately drops all outbound packets at the hypervisor level, effectively cutting off exfiltration. This approach leverages the AWS security group stateful firewall, which evaluates outbound traffic before it leaves the instance, and does not require modifying the instance's OS or network configuration. In a real-world scenario, the engineer would then snapshot the EBS volumes and capture memory using tools like 'LiME' or 'AVML' before any further analysis.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
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
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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: Remove the instance from the target group and apply a security group that denies all traffic. — Option D is correct because removing the instance from the target group immediately stops new traffic from the Application Load Balancer to the instance, while applying a security group that denies all outbound traffic (e.g., a custom security group with no outbound rules) halts any ongoing exfiltration without destroying the instance or its attached EBS volumes. This preserves the forensic evidence (memory, disk, logs) for later analysis, unlike termination or shutdown which could lose volatile data.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Yes — watch for: "best", "immediately / without restart". Signals that multiple options may be partially correct. Choose the option that most directly solves the exact problem described, not the one that sounds most complete.
Read the scenario before looking for a memorised answer.
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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 notices that an EC2 instance is sending outbound traffic to a known malicious IP address. The engineer needs to quickly block all traffic to that IP while preserving the instance for forensic analysis. Which approach is the most effective?
hardWhy B: Modifying the security group to deny outbound traffic to that IP is quick and reversible. Using NACLs is slower and affects subnets. Stopping the instance loses volatile data. Route table modification is not effective for a single IP.
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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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