The answer is to add the malicious URL to the Microsoft Defender for Endpoint custom threat indicator list. This is the correct first response action because it immediately blocks the malicious link across all endpoints using Defender for Endpoint’s indicator of compromise (IOC) capabilities, preventing any other users from clicking it and halting the spread of the attack. On the SC-200 exam, this question tests your understanding of prioritization in incident response—specifically, that containment via blocking the threat vector (the URL) takes precedence over remediation steps like isolating devices or reporting. A common trap is choosing to block the sender, but that only stops future emails, not users who already clicked the link. Remember the memory tip: “Block the link, not the sender” to lock down the attack surface first.
SC-200 Respond to security incidents Practice Question
This SC-200 practice question tests your understanding of respond to security incidents. 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.
You are a security analyst investigating a detected phishing campaign targeting users in your organization. The Microsoft Defender for Office 365 alert indicates that several users clicked on a malicious link. Which action should you take first to prevent further compromise?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "first"
Why it matters: Order matters here. You are being tested on which action comes before the others — not which action is generally useful.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Add the malicious URL to the Microsoft Defender for Endpoint custom threat indicator list.
The first priority is to block the malicious URL across all endpoints using Microsoft Defender for Endpoint's IOC capabilities to prevent any other users from clicking the link. Isolating users would be disruptive and may not be necessary for all. Reporting to Microsoft is not immediate. Blocking the sender may help but does not stop users who already have the email.
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.
✓
Add the malicious URL to the Microsoft Defender for Endpoint custom threat indicator list.
Why this is correct
This blocks the URL across all devices and is the fastest way to prevent further clicks.
Clue confirmation
The clue word "first" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
✗
Isolate all affected users' devices from the network.
Why it's wrong here
Isolation is a drastic step that should be taken only if there is evidence of active exploitation; it is not the first action.
✗
Report the email to Microsoft for analysis.
Why it's wrong here
Reporting is useful for intelligence but does not provide immediate protection.
✗
Block the sender email address in the tenant.
Why it's wrong here
Blocking the sender does not stop users from clicking a link that is already delivered.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Many certification questions include familiar terms but test a specific constraint. Read the exact wording before choosing an answer that is generally true but wrong for this case.
Detailed technical explanation
How to think about this question
This question should be treated as a scenario, not a definition check. Identify the problem, the constraint and the best action. Then compare each option against those facts.
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.
Use explanations to understand the rule behind the answer.
TExam Day Tips
→Underline the problem statement mentally.
→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 healthcare organisation deploys an application with a public-facing web tier and a private database tier. The database subnet has no public IP and only accepts connections from the web tier's security group. Questions like this test whether you can design cloud network isolation using VNets/VPCs, subnets, and security group rules.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this SC-200 question in full detail.
Identify which SC-200 exam domain this question belongs to, then review the specific concept being tested. Practise related questions in that domain and focus on understanding why each wrong answer is tempting — not just why the correct answer is right.
Respond to security incidents — This question tests Respond to security incidents — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Add the malicious URL to the Microsoft Defender for Endpoint custom threat indicator list. — The first priority is to block the malicious URL across all endpoints using Microsoft Defender for Endpoint's IOC capabilities to prevent any other users from clicking the link. Isolating users would be disruptive and may not be necessary for all. Reporting to Microsoft is not immediate. Blocking the sender may help but does not stop users who already have the email.
What should I do if I get this SC-200 question wrong?
Identify which SC-200 exam domain this question belongs to, then review the specific concept being tested. Practise related questions in that domain and focus on understanding why each wrong answer is tempting — not just why the correct answer is right.
Are there clue words in this question I should notice?
Yes — watch for: "first". Order matters here. You are being tested on which action comes before the others — not which action is generally useful.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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