Quick Answer
The answer is intrusion detection system (IDS) and Security Information and Event Management (SIEM). An IDS directly monitors network traffic for malicious patterns or policy violations, triggering alerts when it detects known attack signatures or anomalous behavior, making it a primary tool for identifying unauthorized access in real time. A SIEM, meanwhile, aggregates and correlates logs from diverse sources like firewalls, servers, and IDS, using advanced analytics to spot subtle, coordinated attack patterns that individual logs might miss, thus providing a broader detection capability. On the CISSP exam, this pairing tests your understanding of the detection domain, specifically how passive monitoring (IDS) and centralized log analysis (SIEM) complement each other; a common trap is confusing a firewall’s preventive role with detection. Remember the mnemonic “IDS Sniffs, SIEM Connects” to recall that IDS inspects packets while SIEM correlates events across the network.
This CISSP practice question tests your understanding of security operations. 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.
Which TWO of the following are effective methods for detecting unauthorized access to a network? (Choose two.)
Vulnerability scanner
Why wrong: Identifies weaknesses, not active unauthorized access.
Antivirus software
Why wrong: Detects malware, not unauthorized access directly.
Security information and event management (SIEM)
Correlates logs from multiple sources to detect incidents.
Firewall rule review
Why wrong: Preventive control, not detection-focused.
Intrusion detection system (IDS)
Monitors network traffic for suspicious patterns.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
Security information and event management (SIEM)
A SIEM aggregates and correlates logs from multiple sources (e.g., firewalls, servers, IDS) in real time, enabling detection of anomalous patterns indicative of unauthorized access. It provides centralized visibility and alerting that can identify a breach even when individual logs appear benign.
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.
Vulnerability scanner
Why it's wrong here
Identifies weaknesses, not active unauthorized access.
Antivirus software
Why it's wrong here
Detects malware, not unauthorized access directly.
Security information and event management (SIEM)
Why this is correct
Correlates logs from multiple sources to detect incidents.
Related concept
Read the scenario before looking for a memorised answer.
Firewall rule review
Why it's wrong here
Preventive control, not detection-focused.
Intrusion detection system (IDS)
Why this is correct
Monitors network traffic for suspicious patterns.
Related concept
Read the scenario before looking for a memorised answer.
Common exam traps
The trap here is that candidates confuse vulnerability scanning (proactive) with intrusion detection (reactive), or assume antivirus covers network-level threats, when in fact neither provides real-time monitoring of network access attempts.
Detailed technical explanation
SIEMs use correlation engines with rules (e.g., Sigma or custom logic) to match events like multiple failed logins followed by a successful login from a foreign IP, which may indicate a password-spray attack. IDS systems (network-based or host-based) analyze packet headers and payloads against signatures (e.g., Snort rules) or behavioral baselines to flag suspicious traffic, such as an internal host scanning external IPs, which could signal a compromised device.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
A security team runs a vulnerability scan on a web application and discovers an unpatched SQL injection flaw. The team prioritises remediation by CVSS score — critical flaws are patched within 24 hours, high within 7 days. Questions like this test whether you understand vulnerability management processes, scanning tools, and remediation prioritisation.
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: Security information and event management (SIEM) — A SIEM aggregates and correlates logs from multiple sources (e.g., firewalls, servers, IDS) in real time, enabling detection of anomalous patterns indicative of unauthorized access. It provides centralized visibility and alerting that can identify a breach even when individual logs appear benign.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Read the scenario before looking for a memorised answer.
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Last reviewed: Jun 24, 2026
This CISSP 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 CISSP exam.
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