Quick Answer
The answer is to investigate the source host for signs of compromise. This is the correct first action because a Trojan IDS alert, such as one detecting a possible Zeus variant making an outbound connection, indicates potential command-and-control (C2) traffic; the analyst must validate the alert through host-based analysis—checking processes, registry entries, and active network connections—before taking any containment steps. On the Cisco CyberOps Associate 200-201 exam, this scenario tests your understanding of the incident response process, specifically the priority of verification over reaction. A common trap is jumping to block the IP address, but that can destroy evidence and fail against malware using domain flux. Remember the memory tip: “Verify before you modify”—always confirm compromise on the source host first to preserve forensic integrity and avoid disrupting the investigation.
This 200-201 practice question tests your understanding of network intrusion analysis. 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.
An analyst sees an alert from the IDS: 'ET TROJAN Possible Zeus Variant Outbound Connection'. What action should the analyst 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.
Block the IP address on the firewall
Why wrong: Blocking without investigation may block legitimate traffic.
Ignore the alert as a false positive
Why wrong: Ignoring could miss a real threat.
Investigate the source host for signs of compromise
Investigation confirms if the alert is valid.
Reimage the host immediately
Why wrong: Reimaging is drastic without confirmation.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
Investigate the source host for signs of compromise
Option C is correct because the first priority when an IDS alerts on a possible Zeus variant (a known Trojan) is to investigate the source host to confirm or rule out compromise. Zeus is a credential-stealing Trojan that often establishes outbound C2 (command-and-control) traffic; blindly blocking the IP (A) could disrupt the investigation and may not stop the malware if it uses domain flux or multiple IPs. Reimaging (D) destroys forensic evidence, and ignoring the alert (B) is negligent given the severity of Zeus. The analyst must perform host-based analysis (e.g., check processes, registry, network connections) to validate the alert before taking containment actions.
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.
Block the IP address on the firewall
Why it's wrong here
Blocking without investigation may block legitimate traffic.
Ignore the alert as a false positive
Why it's wrong here
Ignoring could miss a real threat.
Investigate the source host for signs of compromise
Why this is correct
Investigation confirms if the alert is valid.
Clue confirmation
The clue word "first" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
Reimage the host immediately
Why it's wrong here
Reimaging is drastic without confirmation.
Common exam traps
Cisco often tests the principle that IDS/IPS alerts require verification before action—candidates mistakenly choose to block or reimage immediately, but the correct first step is always to investigate the affected host to confirm the alert and preserve evidence.
Detailed technical explanation
Zeus (and its variants like Gameover Zeus) typically uses a peer-to-peer C2 infrastructure or HTTP-based POST requests to exfiltrate stolen credentials. The IDS signature 'ET TROJAN Possible Zeus Variant Outbound Connection' likely triggers on specific HTTP headers, URI patterns, or JA3 fingerprints associated with Zeus traffic. In a real-world scenario, the analyst should first capture a packet capture (PCAP) of the outbound connection, then use tools like Volatility or Sysinternals to inspect the host for malicious processes (e.g., 'sdra64.exe' or 'ntos.exe') before deciding on containment.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
A practitioner preparing for the 200-201 exam encounters this exact type of scenario on the job. The correct answer here is not the most general option — it is the best answer for the specific constraint described. Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option. Real exam questions reward reading the full scenario before eliminating options, because the constraint defines which answer fits.
What to study next
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
Network Intrusion Analysis — This question tests Network Intrusion Analysis — Read the scenario before looking for a memorised answer..
The correct answer is: Investigate the source host for signs of compromise — Option C is correct because the first priority when an IDS alerts on a possible Zeus variant (a known Trojan) is to investigate the source host to confirm or rule out compromise. Zeus is a credential-stealing Trojan that often establishes outbound C2 (command-and-control) traffic; blindly blocking the IP (A) could disrupt the investigation and may not stop the malware if it uses domain flux or multiple IPs. Reimaging (D) destroys forensic evidence, and ignoring the alert (B) is negligent given the severity of Zeus. The analyst must perform host-based analysis (e.g., check processes, registry, network connections) to validate the alert before taking containment actions.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Yes — watch for: "first". Order matters here. You are being tested on which action comes before the others — not which action is generally useful.
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 analyst is reviewing a Snort alert that triggered on the signature 'ET TROJAN Win.Trojan.Generic'. What is the most likely reason this alert fired?
easyWhy A: The Snort signature 'ET TROJAN Win.Trojan.Generic' is designed to detect network traffic patterns or payloads associated with known Trojan malware. When this alert fires, it indicates that the sensor observed data matching the signature's characteristics, most likely from a system that is infected with a Trojan and is communicating with a command-and-control server or performing malicious activity.
Last reviewed: Jun 11, 2026
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