CRISC IT Risk Assessment Practice Question
Which of the following is a detective control for an information system?
⚠ Common exam trap
Test-takers frequently confuse detective controls (which identify incidents after they occur) with preventive controls (which stop incidents before they happen), leading candidates to mistakenly classify firewalls or encryption as detective.
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
✓
Intrusion detection system
An intrusion detection system (IDS) is a detective control because it monitors network traffic or system activity for malicious actions or policy violations and generates alerts when such events occur. Unlike preventive controls, an IDS does not block or stop the attack; it detects and reports it after the fact, enabling incident response.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
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Data backup
Why it's wrong here
Data backup is a corrective or recovery control: it restores data after loss or corruption rather than identifying that an incident occurred. It tempts because backup is a fundamental security safeguard, and would be correct if the question asked how to recover from ransomware, deletion, or hardware failure.
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Encryption
Why it's wrong here
Encryption is a preventive control: it renders data unreadable to unauthorised parties before access occurs, rather than detecting an event after the fact. It tempts because encryption is central to data protection, and would be the right answer if the question asked for a preventive control safeguarding confidentiality at rest or in transit.
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Firewall
Why it's wrong here
A firewall is a preventive control: it blocks or permits traffic according to rules before any malicious packet reaches the target. It tempts because firewalls log blocked connections, yet their primary function is prevention, and would be correct if the question asked for a preventive network boundary control.
- ✓
Intrusion detection system
Why this is correct
An intrusion detection system monitors network or host activity and raises alerts on suspicious patterns, identifying incidents after or during occurrence rather than blocking them. That monitoring-and-alerting function is detective by definition, distinguishing it from preventive controls such as firewalls or encryption.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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