What is the main characteristic of a polymorphic virus?

• A. It replicates itself without any changes.
• B. It requires a hardware key to run.
• C. It changes its code to avoid detection by antivirus software.
• D. It deletes itself after infection.

Answer: (C)

Polymorphic viruses change their code to avoid detection by antivirus software while keeping the same malicious behavior. Each infection uses a different appearance—often by encrypting the payload with a new key and including a differently arranged or re-encrypted decryptor—so the signature that antivirus programs look for keeps changing. The actual payload still runs the same malicious actions, but the surrounding code looks different each time, which makes signature-based detection harder.

This isn’t about reproducing unchanged, needing a hardware key, or deleting itself after infection. Those traits describe different behaviors rather than the mutating code characteristic that defines polymorphism.