Quick Answer
The answer is antivirus software detecting a known malware signature, as this is the most definitive incident indicator during the identification phase. This is because a known malware signature represents a precise, verifiable match against a database of established malicious code, leaving no room for interpretation or false positives related to benign anomalies. On the Certified Information Security Manager CISM exam, this question tests your ability to distinguish between a confirmed compromise and ambiguous events like unusual network traffic or failed logins, which are merely suspicious. A common trap is confusing a potential threat—such as a vulnerability scan—with an actual incident, which requires evidence of exploitation. For a reliable incident indicator, remember the mnemonic “SIG” for Signature, Indicator, and Guarantee: a known signature provides the guaranteed indicator that an incident has occurred.
This CISM practice question tests your understanding of incident management. 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.
During the identification phase of incident response, which of the following is the MOST reliable indicator of a security incident?
A network administrator notices unusual traffic patterns.
Why wrong: Not conclusive; may be benign.
An employee reports slow computer performance.
Why wrong: Could be due to many non-malicious causes.
A vendor sends a vulnerability disclosure.
Why wrong: Indicates a potential risk, not a current incident.
Antivirus software detects a known malware signature.
Direct evidence of malware infection.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
Antivirus software detects a known malware signature.
Option C is correct because antivirus detection of a known malware signature is a definitive indicator. Options A and B are ambiguous. Option D is a potential threat but not an incident.
Key principle: NAT direction and interface roles matter as much as the IP address mapping. Inside/outside designation controls which traffic is translated.
Answer analysis
For each option: why learners choose it and why it is or isn't the right answer here.
A network administrator notices unusual traffic patterns.
Why it's wrong here
Not conclusive; may be benign.
An employee reports slow computer performance.
Why it's wrong here
Could be due to many non-malicious causes.
A vendor sends a vulnerability disclosure.
Why it's wrong here
Indicates a potential risk, not a current incident.
Antivirus software detects a known malware signature.
Why this is correct
Direct evidence of malware infection.
Related concept
Static NAT maps one inside address to one outside address.
Common exam traps
NAT is not only about the public address. The inside/outside interface roles and the ACL or rule that matches traffic are just as important.
Detailed technical explanation
NAT questions usually test address translation, overload/PAT behaviour, static mappings and whether the right traffic is being translated. Read the interface direction and address terms carefully.
Key takeaway
NAT direction and interface roles matter as much as the IP address mapping. Inside/outside designation controls which traffic is translated.
Real-world example
A small business has 20 workstations on the 192.168.1.0/24 network and one public IP from its ISP. The router uses PAT (NAT overload) so all 20 devices share one public address using different source ports. NAT questions test whether you understand the four address terms and which direction each translation applies.
What to study next
Review the four NAT address types (inside local, inside global, outside local, outside global), PAT port overload, and static vs dynamic NAT use cases. Then practise related CISM NAT questions on configuration and troubleshooting.
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FAQ
Incident Management — This question tests Incident Management — Static NAT maps one inside address to one outside address..
The correct answer is: Antivirus software detects a known malware signature. — Option C is correct because antivirus detection of a known malware signature is a definitive indicator. Options A and B are ambiguous. Option D is a potential threat but not an incident.
Review the four NAT address types (inside local, inside global, outside local, outside global), PAT port overload, and static vs dynamic NAT use cases. Then practise related CISM NAT questions on configuration and troubleshooting.
Static NAT maps one inside address to one outside address.
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Last reviewed: Jun 24, 2026
This CISM practice question is part of Courseiva's free ISACA 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 CISM exam.
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