The correct answer is that the write blocker malfunctioned and allowed writes to the original drive. A hash mismatch after forensic imaging directly proves that the source data and the image file are not bit-for-bit identical, which can only occur if the original drive was altered during the acquisition process. Since a write blocker’s sole purpose is to prevent any modification to the evidence, a malfunction that permits writes would change the source data after the initial hash was computed, causing the final hash of the original drive to differ from the hash of the image taken at a later time. On the CHFI exam, this question tests your understanding of forensic imaging integrity and the critical role of hardware write blockers; a common trap is assuming the mismatch is due to a bad cable or software error, but the most direct cause is always unauthorized writes to the source. Memory tip: “If the hash doesn’t match, the blocker didn’t catch.”
CHFI Evidence Acquisition and Duplication Practice Question
This CHFI practice question tests your understanding of evidence acquisition and duplication. 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 imaging a suspect's hard drive using a write blocker and dd command. After imaging, you verify the hash of the original drive and the image file. The original drive hash is SHA1: A1B2C3D4E5..., and the image hash is SHA1: F6G7H8I9J0... What is the most likely cause of the mismatch?
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
✓
The write blocker malfunctioned and allowed writes to the original drive
The hash mismatch indicates that the data on the original drive and the image file are not identical. A write blocker malfunction that allowed writes to the original drive during the imaging process would alter the source data after the initial hash was computed, causing the final hash of the original drive to differ from the hash of the image file taken at a different point in time. This is the most direct cause of a hash mismatch because the write blocker's primary purpose is to prevent any modification to the evidence.
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 dd command used a different block size
Why it's wrong here
Block size does not affect the hash if the same data is read.
✓
The write blocker malfunctioned and allowed writes to the original drive
Why this is correct
If the original drive was modified during acquisition, the hashes will differ.
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 dd command compressed the output
Why it's wrong here
dd does not compress by default; compression would not cause a hash mismatch.
✗
The image file was corrupted during transfer
Why it's wrong here
Corruption would likely cause read errors, not a clean hash mismatch.
Common exam traps
Common exam trap: answer the scenario, not the keyword
EC-Council often tests the misconception that dd's block size or compression affects the hash, but the trap here is that candidates overlook the write blocker's role in preserving evidence integrity and instead focus on technical details of the dd command that do not alter the data content.
Detailed technical explanation
How to think about this question
Write blockers operate at the hardware or firmware level to intercept and block write commands (e.g., SCSI commands like WRITE(10) or ATA commands like WRITE DMA) from reaching the storage device. A malfunction could occur due to a faulty bridge chip, improper power cycling, or a driver conflict, allowing a write command to modify the source drive's data after the initial hash was computed. In forensic practice, hashes are often computed both before and after imaging to detect such changes, and a mismatch would invalidate the entire acquisition, requiring re-imaging with a verified write blocker.
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 practitioner preparing for the CHFI 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.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this CHFI question in full detail.
Evidence Acquisition and Duplication — This question tests Evidence Acquisition and Duplication — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The write blocker malfunctioned and allowed writes to the original drive — The hash mismatch indicates that the data on the original drive and the image file are not identical. A write blocker malfunction that allowed writes to the original drive during the imaging process would alter the source data after the initial hash was computed, causing the final hash of the original drive to differ from the hash of the image file taken at a different point in time. This is the most direct cause of a hash mismatch because the write blocker's primary purpose is to prevent any modification to the evidence.
What should I do if I get this CHFI 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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