This CEH practice question tests your understanding of footprinting, reconnaissance and scanning. 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.
An attacker uses a technique where they send a SYN packet with a spoofed source IP address to the target, and the target responds with SYN/ACK to the spoofed IP. The attacker never completes the handshake. This technique is known as:
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "never"
Why it matters: Absolute qualifier. True only if the statement has zero exceptions — be cautious of options that seem obvious but break down in edge cases.
SYN flood
Why wrong: SYN flood is a DoS attack that consumes resources, not a stealth scan.
TCP connect scan
Why wrong: TCP connect scan completes the full handshake, not spoofing.
Idle scan
Idle scan uses a zombie host and spoofed IP to infer open ports from IPID changes.
Half-open scan
Why wrong: Half-open scan (SYN scan) sends SYN, receives SYN/ACK, then sends RST, but doesn't spoof IP.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
Idle scan
The idle scan (option C) is correct because it uses a spoofed SYN packet with a zombie host's IP address to probe open ports on the target. The target sends a SYN/ACK to the zombie, but the attacker never completes the handshake; instead, the attacker monitors the zombie's IPID (IP Identification) field to infer whether the target's port is open or closed. This technique is defined in RFC 793 and leverages the zombie's predictable IPID sequence to perform a blind, stealthy scan.
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.
SYN flood
Why it's wrong here
SYN flood is a DoS attack that consumes resources, not a stealth scan.
TCP connect scan
Why it's wrong here
TCP connect scan completes the full handshake, not spoofing.
Idle scan
Why this is correct
Idle scan uses a zombie host and spoofed IP to infer open ports from IPID changes.
Clue confirmation
The clue word "never" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
Half-open scan
Why it's wrong here
Half-open scan (SYN scan) sends SYN, receives SYN/ACK, then sends RST, but doesn't spoof IP.
Common exam traps
The trap here is that candidates confuse the idle scan with a half-open scan because both involve not completing the handshake, but the idle scan uniquely requires a spoofed source IP and a zombie host to measure IPID changes, whereas a half-open scan uses the attacker's own IP and sends a RST directly.
Detailed technical explanation
Under the hood, the idle scan requires a zombie host with a globally predictable IPID (e.g., incrementing by 1 per packet, as seen in older Windows or Linux kernels). The attacker sends a SYN/ACK to the zombie to record its current IPID, then sends a spoofed SYN to the target with the zombie's IP; if the target's port is open, it sends a SYN/ACK to the zombie, causing the zombie to send a RST and increment its IPID by 1. By re-probing the zombie's IPID, the attacker detects the increment, revealing the open port. In modern systems with randomized IPID (e.g., Linux 3.x+), this technique fails, making it a legacy but exam-relevant method.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
A practitioner preparing for the CEH exam encounters this exact type of scenario on the job. The correct answer here is not the most general option — it is the best answer for the specific constraint described. Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option. Real exam questions reward reading the full scenario before eliminating options, because the constraint defines which answer fits.
What to study next
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Footprinting, Reconnaissance and Scanning — study guide chapter
Learn the concepts, then practise the questions
Footprinting, Reconnaissance and Scanning practice questions
Targeted practice on this topic area only
All CEH questions
1,010 questions across all exam domains
Certified Ethical Hacker CEH study guide
Full concept coverage aligned to exam objectives
CEH practice test guide
How to use practice tests most effectively before exam day
Related practice questions
Use these pages to review the topic behind this question. This is how one missed question becomes focused revision.
Practise CEH questions linked to Footprinting, Reconnaissance and Scanning.
Practise CEH questions linked to Enumeration and System Hacking.
Practise CEH questions linked to Malware, Social Engineering and Network Attacks.
Practise CEH questions linked to Web Application and Injection Attacks.
Practise CEH questions linked to Introduction to Ethical Hacking.
Practise CEH questions linked to Scanning Networks and Enumeration.
Practise CEH questions linked to Vulnerability Analysis and System Hacking.
Practise CEH questions linked to Advanced Topics: Wireless, Cloud, IoT, Cryptography.
Practise CEH questions linked to Footprinting and Reconnaissance.
Practise CEH questions linked to Network and Web Application Attacks.
Practise CEH questions linked to Wireless, IoT and Cloud Security.
Practise CEH questions linked to Cryptography and Malware Analysis.
Practice this exam
Short sessions build daily habit. Longer sessions build exam-day stamina. Try a timed session to simulate real conditions.
FAQ
Footprinting, Reconnaissance and Scanning — This question tests Footprinting, Reconnaissance and Scanning — Read the scenario before looking for a memorised answer..
The correct answer is: Idle scan — The idle scan (option C) is correct because it uses a spoofed SYN packet with a zombie host's IP address to probe open ports on the target. The target sends a SYN/ACK to the zombie, but the attacker never completes the handshake; instead, the attacker monitors the zombie's IPID (IP Identification) field to infer whether the target's port is open or closed. This technique is defined in RFC 793 and leverages the zombie's predictable IPID sequence to perform a blind, stealthy scan.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Yes — watch for: "never". Absolute qualifier. True only if the statement has zero exceptions — be cautious of options that seem obvious but break down in edge cases.
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 →
Last reviewed: Jun 24, 2026
This CEH practice question is part of Courseiva's free EC-Council 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 CEH 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.