The correct answer is that a polymorphic virus uses encryption with a variable key and mutates its code while preserving its original functionality. This mutation is driven by a built-in mutation engine that alters the virus’s decryption routine and encrypted payload each time it replicates, creating a completely new signature for every infection. Because the virus body is encrypted and the decryption routine changes, signature-based antivirus tools cannot recognize it based on static patterns. On the Certified Ethical Hacker CEH exam, this concept tests your understanding of advanced evasion techniques, often appearing in questions about malware types and antivirus bypass methods. A common trap is confusing a polymorphic virus with a metamorphic virus—remember that polymorphic viruses use encryption with a variable key, while metamorphic viruses rewrite their entire code without encryption. Memory tip: think “Poly = many forms, using a key that changes.”
CEH Cryptography and Malware Analysis Practice Question
This CEH practice question tests your understanding of cryptography and malware analysis. 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 of the following are characteristics of a polymorphic virus? (Choose two.)
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Mutates its code to evade signature detection
Option B is correct because a polymorphic virus mutates its code—typically by using a mutation engine—while preserving its original functionality. This mutation changes the virus's signature each time it replicates, allowing it to evade signature-based detection by antivirus software. Option C is correct because polymorphic viruses commonly use encryption with a variable key; the virus body is encrypted, and the decryption routine mutates, so the encrypted payload looks different with each infection.
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.
✗
Remains constant in code to ensure replication
Why it's wrong here
Polymorphic viruses change constantly.
✓
Mutates its code to evade signature detection
Why this is correct
Polymorphic viruses change their code pattern each time they replicate.
Related concept
Read the scenario before looking for a memorised answer.
✓
Uses encryption with a variable key
Why this is correct
Polymorphic viruses often use a variable encryption key to change the decrypted code.
Related concept
Read the scenario before looking for a memorised answer.
✗
Spreads via network shares
Why it's wrong here
That is typical of worms, not specifically polymorphic viruses.
✗
Resides in the boot sector of a hard drive
Why it's wrong here
That describes a boot sector virus.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often confuse 'polymorphic' with 'metamorphic' or assume that all viruses that use encryption are polymorphic, but the key distinction is that polymorphic viruses use a variable key and mutate the decryption routine, whereas simple encrypted viruses use a fixed key and do not change their decryptor.
Detailed technical explanation
How to think about this question
Under the hood, a polymorphic virus includes a mutation engine that generates new decryption routines and re-encrypts the virus body with a different key each time. This means the virus's binary pattern changes on every infection, but the decryption engine must remain functional—often using obfuscation techniques like garbage code insertion or instruction substitution. In real-world scenarios, advanced polymorphic malware like the 'Storm Worm' used this technique to evade early antivirus signatures, requiring heuristic or behavioral analysis to detect.
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 CEH question in full detail.
Cryptography and Malware Analysis — This question tests Cryptography and Malware Analysis — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Mutates its code to evade signature detection — Option B is correct because a polymorphic virus mutates its code—typically by using a mutation engine—while preserving its original functionality. This mutation changes the virus's signature each time it replicates, allowing it to evade signature-based detection by antivirus software. Option C is correct because polymorphic viruses commonly use encryption with a variable key; the virus body is encrypted, and the decryption routine mutates, so the encrypted payload looks different with each infection.
What should I do if I get this CEH 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 CEH 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 CEH 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.