hardMultiple Choice
CISA Practice Question: A company's endpoint protection solution alerts…
A company's endpoint protection solution alerts on a file that is digitally signed by a trusted software vendor but exhibits malicious behavior on execution. What type of threat does this scenario most likely depict?
⚠ Common exam trap
Test-takers frequently confuse 'signed malware' with a 'Trojan horse,' but the critical differentiator is the presence of a valid digital signature from a trusted vendor, which is not inherent to Trojans and is the specific mechanism that makes this threat unique.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Signed malware, indicating the certificate may have been compromised.
The scenario describes a file that is digitally signed by a trusted vendor yet exhibits malicious behavior. This is the classic definition of signed malware, where the digital certificate used to sign the file has likely been stolen, misused, or issued fraudulently. The trusted signature bypasses reputation-based and allowlist controls, making the threat particularly dangerous because the file appears legitimate to security tools that trust the vendor's certificate.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
A Trojan horse disguised as legitimate software.
Why it's wrong here
A valid vendor signature with malicious execution indicates the vendor's signing key or update channel was compromised, or the binary was trojanised — supply-chain compromise, not a Trojan posing as legitimate software. It is tempting because signed malware resembles a Trojan, but Trojans impersonate trusted software without genuine vendor signatures.
- ✓
Signed malware, indicating the certificate may have been compromised.
Why this is correct
A valid vendor certificate means the binary passes signature checks, so detection relies on behaviour rather than reputation; malicious code signed with a compromised or misused certificate is signed malware. This matches the stem's trusted-signature-but-malicious-execution scenario.
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A zero-day exploit targeting an unpatched vulnerability.
Why it's wrong here
A zero-day exploits an unpatched software vulnerability; here the file is validly signed and runs as intended, so no vulnerability is exploited. It is tempting because signed malware evades signature detection, but zero-day would be correct where an unknown flaw is exploited before a patch exists.
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A fileless attack that never writes to disk.
Why it's wrong here
The stem describes a validly signed executable that turns malicious at runtime, which is a signed-binary or trojanised-software threat. Fileless attacks execute in memory via scripting or LOLBins and typically leave no signed file on disk, so the trusted signature contradicts this. Fileless detection would be the answer if no file were written.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This CISA practice question is part of Courseiva's free ISACA 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 CISA exam.