SC-100 Practice Question: Design security solutions for applications and data
Exhibit
Log Analytics query: SecurityEvent | where TimeGenerated > ago(24h) | where AccountType == "User" | summarize FailedLogins = count() by Account, Computer | where FailedLogins > 5
Refer to the exhibit. You are investigating a security incident in Microsoft Sentinel. The KQL query above is used to identify potential brute-force attacks. What does the query return?
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
✓
A list of user accounts and computers where the account has more than 5 failed logins in the last 24 hours.
The correct answer is C: a list of user accounts and computers where the account has more than 5 failed logins in the last 24 hours. This matches a typical Sentinel brute-force KQL pattern that filters SecurityEvent for EventID 4625 (failed logon), restricts the TimeGenerated window to the last 24 hours, and then summarizes failed attempts by Account and Computer, filtering with a threshold greater than 5. Option A is wrong because the grouping is by account and computer, not by computer alone, and it ignores the 24-hour time window. Option B is wrong because it omits the per-computer grouping, so it would not return computer context. Option D is wrong because it references successful logins rather than failed logons (EventID 4625).
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
A list of computers with more than 5 failed logins from any account.
Why it's wrong here
The query groups by user account, so its output lists accounts rather than computers. Grouping failures by computer is tempting because it exposes a single host receiving many failed attempts, and would be correct when investigating a machine targeted by brute-force activity from many usernames.
- ✗
A list of user accounts with more than 5 failed logins across all computers.
Why it's wrong here
The query summarises results per computer, not per user account, so it cannot return a user-based list. Aggregating failed logins by account is tempting because it identifies targeted usernames, and would be correct when the goal is finding accounts subjected to repeated authentication failures.
- ✓
A list of user accounts and computers where the account has more than 5 failed logins in the last 24 hours.
Why this is correct
The query aggregates failed sign-in events by user and computer, then filters with a count greater than five within a 24-hour window. This threshold and time constraint directly satisfy the brute-force detection scenario, returning the affected account and host pairs.
- ✗
A list of user accounts with more than 5 successful logins in the last 24 hours.
Why it's wrong here
The query filters failed sign-in attempts, so successful logins never appear in its output. Counting successful authentications is tempting because it can reveal password-spraying that eventually succeeds, and would be correct when hunting for accounts compromised after many valid logins.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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