Quick Answer
The answer is a SYN scan. This is correct because a SYN scan, also known as a half-open scan, sends TCP SYN packets to a specific port on multiple hosts without completing the three-way handshake; if the target responds with a SYN-ACK, the port is open, but the attacker immediately sends a RST to abort the connection, making it stealthier than a full connect scan. On the ISC2 Certified in Cybersecurity CC exam, this scenario tests your ability to differentiate reconnaissance techniques from denial-of-service attacks—a common trap is confusing a SYN flood (which overwhelms a single host) with a SYN scan (which probes many hosts). The key clue in the alert is the single external IP targeting the same port across multiple internal hosts, which is the hallmark of port scanning for open services. Memory tip: think “SYN scan = scan for open doors” versus “SYN flood = flood the door with knocks.”
This CC 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.
A security analyst is reviewing an alert from the IDS that shows a large number of TCP SYN packets sent to a single port on multiple internal hosts from a single external IP address. The analyst suspects a reconnaissance attack. Which type of attack is this most likely?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "most likely"
Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
SYN flood
Why wrong: A SYN flood aims to overwhelm the target with half-open connections, not just scan.
Ping sweep
Why wrong: A ping sweep uses ICMP echo requests to identify live hosts, not TCP SYN packets.
Smurf attack
Why wrong: A Smurf attack uses ICMP echo replies to amplify traffic, not TCP SYN packets.
SYN scan
A SYN scan sends TCP SYN packets to determine which ports are open, characteristic of reconnaissance.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
SYN scan
This is most likely a SYN scan (option D), a reconnaissance technique where an attacker sends TCP SYN packets to a specific port on multiple hosts to determine if the port is open. A SYN scan is stealthier than a full TCP connect scan because it never completes the three-way handshake, leaving fewer logs. The IDS alert describes the hallmark behavior of a SYN scan: a single external IP targeting the same port across many internal hosts.
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
A SYN flood aims to overwhelm the target with half-open connections, not just scan.
Ping sweep
Smurf attack
SYN scan
Why this is correct
A SYN scan sends TCP SYN packets to determine which ports are open, characteristic of reconnaissance.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
Common exam traps
ISC2 often tests the distinction between a SYN flood (DoS) and a SYN scan (reconnaissance), and the trap here is that candidates confuse the use of SYN packets in a volumetric attack versus a probing technique.
Detailed technical explanation
A SYN scan (also called half-open scan) sends a SYN packet and, upon receiving a SYN-ACK (indicating an open port), sends an RST to tear down the connection before it is fully established, avoiding completion of the three-way handshake. This technique bypasses some application-level logging and can evade basic firewalls that only log established connections. In practice, modern IDS/IPS systems can detect SYN scans by tracking the rate of SYN packets without corresponding ACKs, but the core behavior remains a reconnaissance staple.
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: SYN scan — This is most likely a SYN scan (option D), a reconnaissance technique where an attacker sends TCP SYN packets to a specific port on multiple hosts to determine if the port is open. A SYN scan is stealthier than a full TCP connect scan because it never completes the three-way handshake, leaving fewer logs. The IDS alert describes the hallmark behavior of a SYN scan: a single external IP targeting the same port across many internal hosts.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Yes — watch for: "most likely". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
Read the scenario before looking for a memorised answer.
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Last reviewed: Jun 30, 2026
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