This CS0-003 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 small business with 50 employees uses a single Windows Server 2019 as a domain controller and file server. The company recently experienced a ransomware attack that encrypted all files on the server. The IT manager restored the files from a backup that was taken two days before the attack. However, the next day, the files were encrypted again. The analyst suspects the ransomware may have persisted or re-entered. The network is air-gapped from the internet, but employees use USB drives. Which of the following is the MOST likely reason for the re-infection?
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.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
An employee inserted an infected USB drive after the restoration.
Option B is correct because the network is air-gapped from the internet, leaving USB drives as the primary vector for reintroducing malware. If an employee inserted an infected USB drive after the restoration, the ransomware could execute and re-encrypt the files. The air-gap eliminates internet-based re-entry, and the backup was clean since it restored files without immediate re-encryption until the next day.
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.
✗
The backup itself contained the ransomware.
Why it's wrong here
Backup was from before the attack, so should be clean unless ransomware was present before.
✓
An employee inserted an infected USB drive after the restoration.
Why this is correct
With air-gap, USB is the only vector for re-introduction.
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.
✗
The ransomware was still active in memory on the server.
Why it's wrong here
Restoration process usually involves reboot, which clears memory.
✗
The domain controller was not fully patched.
Why it's wrong here
Patching would not prevent an infected USB.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates may assume the backup was infected (Option A) or that patching (Option D) is the root cause, but the air-gap and USB vector point directly to physical media reintroduction, not network-based persistence or patch status.
Detailed technical explanation
How to think about this question
Ransomware often uses persistence mechanisms like scheduled tasks or registry run keys to survive reboots, but a full system restore from backup typically replaces the entire OS volume, removing those artifacts. In air-gapped environments, USB drives are a common infection vector because they bypass network controls; the ransomware may have been dormant on a USB drive and executed when the employee plugged it in after restoration. This scenario highlights the importance of scanning all removable media before use, even in isolated networks.
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 developer is choosing between AES-256 (symmetric) and RSA-2048 (asymmetric) for encrypting a large file that will be sent to a partner. Symmetric encryption is fast but requires key exchange; asymmetric is slower but solves the key distribution problem. A hybrid approach — encrypt the file with AES, encrypt the AES key with RSA — is standard. Questions like this test whether you understand when each approach applies.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this CS0-003 question in full detail.
Security Operations — This question tests Security Operations — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: An employee inserted an infected USB drive after the restoration. — Option B is correct because the network is air-gapped from the internet, leaving USB drives as the primary vector for reintroducing malware. If an employee inserted an infected USB drive after the restoration, the ransomware could execute and re-encrypt the files. The air-gap eliminates internet-based re-entry, and the backup was clean since it restored files without immediate re-encryption until the next day.
What should I do if I get this CS0-003 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Are there clue words in this question I should notice?
Yes — watch for: "most likely". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Question Discussion
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