The correct answers are encryption with a variable key and polymorphic code, as both techniques are specifically designed to evade signature-based antivirus detection by ensuring no static byte sequence remains constant across malware samples. Polymorphic code mutates its decryption loop with each infection while preserving the original malicious payload, generating functionally equivalent but bytewise different code that defeats static signature matching. Encryption with a variable key changes the decryption key per sample, producing different ciphertext each time and thus preventing antivirus from recognizing the encrypted payload. On the CHFI exam, this concept tests your understanding of how packed malware obfuscates itself to bypass forensic analysis and endpoint protection—a common trap is confusing simple encryption with a fixed key, which does not evade detection because the ciphertext remains identical. Memory tip: think "same payload, different wrapper"—the payload stays the same, but the code and key change every time.
CHFI Malware Forensics Practice Question
This CHFI practice question tests your understanding of malware forensics. 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.
Which TWO techniques are commonly used to evade detection by antivirus software in packed malware?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Polymorphic code
Polymorphic code (C) is correct because it mutates its decryption loop with each infection while preserving the original malicious payload, generating functionally equivalent but bytewise different code. This signature mutation evades signature-based antivirus detection by ensuring no static byte sequence remains constant across samples. Encryption with a variable key (E) is correct because it changes the decryption key per sample, producing different ciphertext each time and thus defeating signature matching on the encrypted payload.
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.
✗
Code obfuscation
Why it's wrong here
Obfuscation makes code hard to read but is not a packing-specific evasion technique.
✗
Anti-debugging tricks
Why it's wrong here
Anti-debugging is a runtime evasion technique, not a packing evasion.
✓
Polymorphic code
Why this is correct
Polymorphic code mutates its signature, evading signature-based detection.
Related concept
Read the scenario before looking for a memorised answer.
✗
Anti-VM checks
Why it's wrong here
Anti-VM checks detect sandboxes, not directly a packing technique.
✓
Encryption with a variable key
Why this is correct
Encryption hides the payload; variable keys prevent static analysis.
Related concept
Read the scenario before looking for a memorised answer.
Common exam traps
Common exam trap: answer the scenario, not the keyword
EC-Council often tests the distinction between polymorphic code (which changes the decryption stub) and metamorphic code (which rewrites the entire payload), and candidates confuse anti-debugging or anti-VM techniques with signature evasion methods.
Detailed technical explanation
How to think about this question
Polymorphic engines typically use a mutable decryption stub that generates random instructions (e.g., NOP sleds, register swaps) while the encrypted payload remains constant; the stub is decrypted at runtime to execute the original code. In contrast, metamorphic code rewrites the entire payload, not just the stub, making it even harder to detect. Real-world examples like the Storm Worm used polymorphic packing to produce millions of unique hashes, overwhelming signature databases.
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 small business has 20 workstations on the 192.168.1.0/24 network and one public IP from its ISP. The router uses PAT (NAT overload) so all 20 devices share one public address using different source ports. NAT questions test whether you understand the four address terms and which direction each translation applies.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this CHFI question in full detail.
Malware Forensics — This question tests Malware Forensics — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Polymorphic code — Polymorphic code (C) is correct because it mutates its decryption loop with each infection while preserving the original malicious payload, generating functionally equivalent but bytewise different code. This signature mutation evades signature-based antivirus detection by ensuring no static byte sequence remains constant across samples. Encryption with a variable key (E) is correct because it changes the decryption key per sample, producing different ciphertext each time and thus defeating signature matching on the encrypted payload.
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.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
About these practice questions
Courseiva creates original exam-style practice questions with explanations and wrong-answer analysis. It does not publish real exam questions, exam dumps, or protected exam content. Learn why practice questions differ from exam dumps →
Share a tip, memory trick, or ask about the reasoning behind this question. Do not post real exam questions, leaked content, braindumps, or copyrighted exam material. Comments are moderated and may be removed without notice.
This CHFI practice question is part of Courseiva's free EC-Council certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the CHFI exam.
Question Discussion
Share a tip, memory trick, or ask about the reasoning behind this question. Do not post real exam questions, leaked content, braindumps, or copyrighted exam material. Comments are moderated and may be removed without notice.
Sign in to join the discussion.