Quick Answer
The answer is detect and alert on potential security incidents. This is correct because an intrusion detection system (IDS) is a passive monitoring technology that analyzes network traffic or system activity for signs of malicious behavior or policy violations, but it does not take inline action to block traffic—its primary purpose is to detect suspicious activity and generate alerts for security personnel to investigate and respond. On the ISC2 Certified in Cybersecurity CC exam, this distinction between an IDS and an intrusion prevention system (IPS) is a frequent test point; a common trap is assuming an IDS can automatically block threats, when in fact only an IPS can do that. To remember, think of the IDS as a security camera that watches and warns, not a guard that stops the intruder.
This CC practice question tests your understanding of security operations. Match the stated requirement to the specific cloud service, access model, or configuration option — many options are valid in isolation but not for this scenario. 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 deploys a new intrusion detection system (IDS) on the internal network. Which of the following best describes the primary purpose of this system?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "best"
Why it matters: Signals that multiple options may be partially correct. Choose the option that most directly solves the exact problem described, not the one that sounds most complete.
Clue: "primary"
Why it matters: Asks for the main purpose or function, not a secondary benefit. Eliminate answers that describe side-effects or partial functions.
Block malicious traffic in real time.
Why wrong: Blocking is the function of an intrusion prevention system (IPS).
Detect and alert on potential security incidents.
The core function of an IDS is detection and alerting.
Encrypt sensitive data at rest.
Why wrong: Encryption is a data protection control, not related to IDS.
Prevent unauthorized access to the network.
Why wrong: Prevention is typically done by firewalls and IPS, not IDS.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
Detect and alert on potential security incidents.
An intrusion detection system (IDS) is a passive monitoring technology that analyzes network traffic or system activity for signs of malicious behavior or policy violations. Unlike an intrusion prevention system (IPS), an IDS does not take inline action to block traffic; its primary purpose is to detect suspicious activity and generate alerts for security personnel to investigate and respond.
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 malicious traffic in real time.
Why it's wrong here
Blocking is the function of an intrusion prevention system (IPS).
Detect and alert on potential security incidents.
Why this is correct
The core function of an IDS is detection and alerting.
Clue confirmation
The clue words "best", "primary" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
Encrypt sensitive data at rest.
Why it's wrong here
Encryption is a data protection control, not related to IDS.
Prevent unauthorized access to the network.
Common exam traps
ISC2 often tests the distinction between IDS and IPS, where candidates mistakenly assume an IDS can block traffic because they conflate detection with prevention.
Detailed technical explanation
An IDS typically uses signature-based detection (matching traffic against known attack patterns, e.g., Snort rules), anomaly-based detection (establishing a baseline and flagging deviations), or a hybrid approach. In a real-world scenario, an IDS might detect a SQL injection attempt by matching the payload against a signature like '1=1' in HTTP requests, but it cannot drop the packet; it relies on the security team to correlate the alert with other logs and manually block the attacker's IP via a firewall rule.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
A SOC analyst notices unusual lateral movement in the network at 2 AM. The IR playbook dictates: identify and contain (isolate the affected machine), then eradicate (remove the malware), then recover (restore from backup), then document. Skipping containment before eradication risks the attacker regaining access. Questions like this test the sequence and rationale of incident response phases.
What to study next
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FAQ
Security Operations — This question tests Security Operations — Read the scenario before looking for a memorised answer..
The correct answer is: Detect and alert on potential security incidents. — An intrusion detection system (IDS) is a passive monitoring technology that analyzes network traffic or system activity for signs of malicious behavior or policy violations. Unlike an intrusion prevention system (IPS), an IDS does not take inline action to block traffic; its primary purpose is to detect suspicious activity and generate alerts for security personnel to investigate and respond.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Yes — watch for: "best", "primary". Signals that multiple options may be partially correct. Choose the option that most directly solves the exact problem described, not the one that sounds most complete.
Read the scenario before looking for a memorised answer.
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Last reviewed: Jun 30, 2026
This CC practice question is part of Courseiva's free ISC2 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 CC exam.
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