A false negative occurs when a security control or scanning tool fails to detect a vulnerability that actually exists. In vulnerability scanning, this means the scan reports a system as secure even though it is vulnerable. Therefore, a result that shows no known vulnerability is an example of a false negative if a vulnerability is present but undetected.

CompTIA Security+ SY0-701 explains that false negatives are particularly dangerous because they provide a false sense of security, potentially leaving systems exposed to exploitation. Causes of false negatives include outdated vulnerability signatures, misconfigured scanners, credentialed scan failures, or unsupported legacy systems.

Option A describes a false positive, where a vulnerability is reported but does not exist. Option B may indicate an outdated scan result, not necessarily a false negative. Option D is incorrect because zero-day vulnerabilities do not have known remediations and are typically not detected by signature-based scanners.

Thus, the correct example of a false negative is C: A result that shows no known vulnerability.