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CS0-003 Practice Question: A security analyst at a small company notices…
A security analyst at a small company notices that several workstations in the finance department are communicating with an external IP address known to be associated with a command-and-control server. The analyst checks the host-based firewall logs and sees that outbound connections to that IP are allowed. Which of the following is the BEST immediate action to take?
⚠ Common exam trap
CS0-004 often tests the ordering of incident response steps, tricking candidates into choosing remediation actions (blocking, scanning, updating) before containment (isolating the host).
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
✓
Disconnect the workstations from the network.
Disconnecting the workstations from the network immediately stops the active command-and-control communication and prevents further data exfiltration or lateral movement, which is the priority during a suspected active compromise. Containment precedes remediation, so isolating the hosts is the correct first action before blocking IPs, updating signatures, or scanning. This preserves the ability to perform forensics while halting the threat.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
Disconnect the workstations from the network.
Why this is correct
Isolating the hosts immediately severs the active command-and-control channel, halting data exfiltration or payload retrieval. Since the host-based firewall already permits that outbound traffic, containment must happen at the network layer; disconnecting the workstations is the fastest way to stop ongoing compromise before forensic investigation begins.
- ✗
Block the IP at the perimeter firewall.
Why it's wrong here
Perimeter blocking stops the traffic but leaves the compromised workstations infected and the root cause unaddressed; containment should isolate the hosts and begin investigation. Perimeter blocking is tempting because it is fast and centralised, and it is correct when many hosts share one indicator, but here the affected endpoints need direct remediation.
- ✗
Update the antivirus definitions.
Why it's wrong here
Updating antivirus definitions does not sever the active outbound connection to the command-and-control server, so exfiltration continues during the update cycle. Definitions are for detecting known malware signatures on endpoints, which is the right action after containment, not the immediate response to live C2 traffic.
- ✗
Run a full antivirus scan on the affected workstations.
Why it's wrong here
A full antivirus scan is a detection and remediation step that runs after containment; it does not stop the workstations from continuing to communicate with the command-and-control server. Scanning is appropriate once the C2 channel is severed and the scope of infection is being determined.
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Key term
Threat
A threat is any potential danger that could harm a computer system, network, or data, whether from a malicious hacker, a natural disaster, or an accidental mistake.
Key term
Containment
Containment is the incident response phase where security teams isolate a compromised system or network to prevent the threat from spreading further while preserving evidence.
About these practice questions
One of 701 original CS0-004 practice questions on Courseiva, each with a full explanation and wrong-answer analysis — not exam dumps or protected exam content. Learn why practice questions differ from exam dumps →
JA
Written and reviewed by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
Last reviewed September 2026 · checked against the official CompTIA exam blueprint
This CS0-004 practice question is part of Courseiva's free CompTIA 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 CS0-004 exam.