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Threat Detection and Incident Response →mediumMultiple ChoiceObjective-mapped

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 EC2 instances behind an Application Load Balancer (ALB). The security team receives an alert from Amazon GuardDuty that one of the EC2 instances is generating outbound traffic to a known command-and-control (C2) IP address. The instance is part of an Auto Scaling group (ASG) with a minimum of 2 and maximum of 10 instances. The security incident response playbook instructs the team to isolate the compromised instance without affecting the application's availability. The team needs to preserve the instance for forensic analysis. Which action should the team take first?

Clue words in this question

Noticing these words before you look at the options changes how you read each choice.

Clue: "first"
Why it matters: Order matters here. You are being tested on which action comes before the others — not which action is generally useful.
Clue: "minimum / minimize"
Why it matters: Asks for the least resource use — fewest addresses, smallest subnet, lowest overhead. Eliminate over-provisioned options even if they would technically work.

A
Terminate the compromised EC2 instance and allow the ASG to launch a replacement.
Why wrong: Terminating destroys evidence.
B
Detach the EBS root volume from the instance and attach it to a forensic instance.
Why wrong: Does not stop network traffic immediately.
C
Shut down the instance from within the OS using AWS Systems Manager Run Command.
Why wrong: Shutdown may lose volatile data and is not immediate isolation.
D
Remove the instance from the ALB target group and attach a security group that denies all traffic.
Isolates the instance while preserving it for forensics.

Full breakdown with real-world context →

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

✓

Remove the instance from the ALB target group and attach a security group that denies all traffic.

Option D is correct because removing the instance from the ALB target group immediately stops new traffic from reaching the application, while attaching a security group that denies all traffic (e.g., a custom security group with no inbound/outbound rules) effectively isolates the instance at the network layer. This preserves the instance for forensic analysis and does not affect application availability, as the ASG will not automatically terminate the instance (since it is still running and healthy from the ASG's perspective). The ALB will continue to route traffic to the remaining healthy instances in the target group, maintaining service continuity.

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.

✗
Terminate the compromised EC2 instance and allow the ASG to launch a replacement.
Why it's wrong here
Terminating destroys evidence.
✗
Detach the EBS root volume from the instance and attach it to a forensic instance.
Why it's wrong here
Does not stop network traffic immediately.
✗
Shut down the instance from within the OS using AWS Systems Manager Run Command.
Why it's wrong here
Shutdown may lose volatile data and is not immediate isolation.
✓
Remove the instance from the ALB target group and attach a security group that denies all traffic.
Why this is correct
Isolates the instance while preserving it for forensics.
Clue confirmation
The clue words "first", "minimum / minimize" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.

Common exam traps

Common exam trap: answer the scenario, not the keyword

The trap here is that candidates may think terminating the instance (Option A) is the fastest way to stop the threat, but they overlook the requirement to preserve the instance for forensic analysis and the need to maintain application availability by not triggering an ASG replacement prematurely.

Detailed technical explanation

How to think about this question

When an instance is removed from an ALB target group, the ALB stops sending new requests to it, but existing connections may persist until the connection idle timeout (default 60 seconds for HTTP/HTTPS) expires. Attaching a security group that denies all traffic effectively blocks all inbound and outbound traffic at the VPC firewall level, including the C2 communication, without requiring the instance to be stopped or terminated. This approach aligns with the 'isolate and preserve' phase of incident response, allowing later forensic acquisition (e.g., memory dump, volume snapshot) while the instance remains running.

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

An e-commerce site experiences heavy traffic on Black Friday and near-zero traffic during off-peak weeks. Rather than provisioning permanent large VMs, the team uses auto-scaling groups that add capacity automatically under load and reduce it overnight. Questions like this test whether you understand elasticity, availability zones, and cloud compute scaling patterns.

Quick reference

OSI Model Reference

Layer	Name	PDU	Key Protocols / Devices
7	Application	Data	HTTP, HTTPS, DNS, SMTP, FTP, SSH
6	Presentation	Data	TLS / SSL, JPEG, ASCII encoding
5	Session	Data	NetBIOS, RPC, SIP
4	Transport	Segment / Datagram	TCP, UDP
3	Network	Packet	IP, ICMP, OSPF — Routers
2	Data Link	Frame	Ethernet, Wi-Fi, PPP — Switches, Bridges
1	Physical	Bits	Cables, NICs, Hubs, Repeaters

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: Remove the instance from the ALB target group and attach a security group that denies all traffic. — Option D is correct because removing the instance from the ALB target group immediately stops new traffic from reaching the application, while attaching a security group that denies all traffic (e.g., a custom security group with no inbound/outbound rules) effectively isolates the instance at the network layer. This preserves the instance for forensic analysis and does not affect application availability, as the ASG will not automatically terminate the instance (since it is still running and healthy from the ASG's perspective). The ALB will continue to route traffic to the remaining healthy instances in the target group, maintaining service continuity.

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: "first", "minimum / minimize". Order matters here. You are being tested on which action comes before the others — not which action is generally useful.

What is the key concept behind this question?

Read the scenario before looking for a memorised answer.

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