The correct answer is that the idle scan technique uses a zombie host to hide the attacker’s identity. This works by sending packets with the IP ID field set to 0 and the DF (Don’t Fragment) flag to the zombie, which has an incremental IP ID counter; the attacker then probes the target and monitors changes in the zombie’s IP ID to infer open ports, never directly exposing their own IP address. On the ISC2 Certified in Cybersecurity CC exam, this question tests your understanding of stealth scanning and how attackers leverage a passive, third-party host to avoid detection—a common trap is confusing idle scans with simple SYN scans, which do not use a zombie. Remember the key clue: an IP ID of 0 and DF flag together signal the attacker is “borrowing” a zombie’s identity. Memory tip: think “IDle scan, IDentity hidden, ID field zero.”
ISC2 CC Network Security Practice Question
This CC practice question tests your understanding of network security. 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 a security audit, a penetration tester captures network traffic and finds that some packets have the IP ID field set to 0 and the DF (Don't Fragment) flag set. What is this technique attempting to do?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Perform a stealth scan using a zombie host to hide the attacker's identity
Setting the IP ID field to 0 and the DF flag in packets is characteristic of an idle scan (also known as a stealth scan). This technique uses a zombie host (with an incremental IP ID) to probe a target; by sending packets with DF set and IP ID 0 to the zombie, the attacker can observe changes in the zombie's IP ID to infer open ports on the target, thereby hiding the attacker's true IP address.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✗
Spoof the source IP address of the attacker's machine
Why it's wrong here
The attacker's IP is not spoofed; the zombie's IP is used.
✗
Launch a denial-of-service attack against the target
Why it's wrong here
Idle scan is not a DoS; it's a stealth scan.
✓
Perform a stealth scan using a zombie host to hide the attacker's identity
Why this is correct
Idle scan uses IP ID to map a zombie's activity and infer port states.
Related concept
Read the scenario before looking for a memorised answer.
✗
Evade a firewall by fragmenting packets
Why it's wrong here
DF flag prevents fragmentation.
Common exam traps
Common exam trap: answer the scenario, not the keyword
ISC2 often tests the idle scan by focusing on the combination of IP ID 0 and DF flag, leading candidates to mistakenly think it is about fragmentation evasion or simple spoofing, rather than the stealthy reconnaissance technique using a zombie host.
Detailed technical explanation
How to think about this question
The idle scan relies on the predictable increment of the IP ID field in the zombie host's responses (as per RFC 791). The attacker sends a SYN-ACK to the zombie to check its current IP ID, then sends a spoofed SYN packet to the target with the zombie's IP as source; if the target port is open, it sends a SYN-ACK to the zombie, causing the zombie to send an RST and increment its IP ID. The DF flag is set to ensure the zombie's packets are not fragmented, which could alter the IP ID behavior, and IP ID 0 is used in the probe packets to avoid interfering with the zombie's counter.
KKey Concepts to Remember
Read the scenario before looking for a memorised answer.
Find the constraint that changes the correct option.
Eliminate answers that are true in general but not in this case.
TExam Day Tips
→Watch for words such as best, first, most likely and least administrative effort.
→Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
How this comes up in practice
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.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this CC question in full detail.
Network Security — This question tests Network Security — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Perform a stealth scan using a zombie host to hide the attacker's identity — Setting the IP ID field to 0 and the DF flag in packets is characteristic of an idle scan (also known as a stealth scan). This technique uses a zombie host (with an incremental IP ID) to probe a target; by sending packets with DF set and IP ID 0 to the zombie, the attacker can observe changes in the zombie's IP ID to infer open ports on the target, thereby hiding the attacker's true IP address.
What should I do if I get this CC question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
About these practice questions
Courseiva creates original exam-style practice questions with explanations and wrong-answer analysis. It does not publish real exam questions, exam dumps, or protected exam content. Learn why practice questions differ from exam dumps →
Share a tip, memory trick, or ask about the reasoning behind this question. Do not post real exam questions, leaked content, braindumps, or copyrighted exam material. Comments are moderated and may be removed without notice.
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.
Question Discussion
Share a tip, memory trick, or ask about the reasoning behind this question. Do not post real exam questions, leaked content, braindumps, or copyrighted exam material. Comments are moderated and may be removed without notice.
Sign in to join the discussion.