The correct answer is that the instance is communicating with a known command and control server. This finding, Backdoor:EC2/C&CActivity.B!DNS, is triggered when Amazon GuardDuty detects DNS queries from your EC2 instance to a domain mapped in its threat intelligence feeds as part of known command and control (C&C) infrastructure. The “.B!DNS” suffix specifically indicates the detection was made via DNS request analysis rather than network flow logs, meaning the instance is likely compromised and beaconing out to an attacker’s server. On the AWS Certified Security Specialty SCS-C02 exam, this question tests your understanding of how GuardDuty uses integrated threat intelligence to identify compromised resources without needing deep packet inspection. A common trap is confusing this with a network-based finding like “Backdoor:EC2/C&CActivity.B!” which relies on IP reputation; remember that the “DNS” suffix means the detection came from DNS query patterns, not direct IP communication. Memory tip: “DNS = Domain Name System = Domain-based detection” — if you see “.B!DNS”, think “bad domain in the DNS query.”
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 uses Amazon GuardDuty and receives a finding of type 'Backdoor:EC2/C&CActivity.B!DNS' for an EC2 instance. What does this finding indicate?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The instance is communicating with a known command and control server.
The finding 'Backdoor:EC2/C&CActivity.B!DNS' indicates that GuardDuty has detected DNS queries from the EC2 instance to a domain associated with known command and control (C&C) infrastructure. This is based on GuardDuty's threat intelligence feeds that map DNS request patterns to known malicious domains, signaling that the instance may be compromised and communicating with an attacker's server.
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.
✗
The instance is being targeted by an SSH brute force attack.
Why it's wrong here
SSH brute force would be 'UnauthorizedAccess:EC2/SSHBruteForce'.
✓
The instance is communicating with a known command and control server.
Why this is correct
The finding name indicates C&C activity detected via DNS.
Related concept
Read the scenario before looking for a memorised answer.
✗
The instance is exfiltrating data to an S3 bucket.
Why it's wrong here
Data exfiltration to S3 would be detected as a different finding type.
✗
The instance is being used in a DDoS attack.
Why it's wrong here
DDoS typically involves high traffic volumes, not necessarily C&C communication.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates may confuse 'Backdoor:EC2/C&CActivity.B!DNS' with generic network anomalies or other attack types, but the key differentiator is the DNS-specific indicator that pinpoints communication with a known command and control server, not the attack vector or data exfiltration method.
Detailed technical explanation
How to think about this question
GuardDuty uses DNS resolver logs (via VPC Flow Logs or Route 53 Resolver query logs) to inspect outbound DNS queries. The 'C&CActivity.B!DNS' finding specifically matches DNS queries against threat intelligence lists of domains known to host C&C infrastructure, often using domain generation algorithms (DGAs) or fast-flux DNS techniques. This detection is independent of the actual payload traffic, meaning even if the C&C communication is encrypted, the DNS query itself can reveal the malicious intent.
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 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
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.
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: The instance is communicating with a known command and control server. — The finding 'Backdoor:EC2/C&CActivity.B!DNS' indicates that GuardDuty has detected DNS queries from the EC2 instance to a domain associated with known command and control (C&C) infrastructure. This is based on GuardDuty's threat intelligence feeds that map DNS request patterns to known malicious domains, signaling that the instance may be compromised and communicating with an attacker's server.
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.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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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.
Question Discussion
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