OS identification in tools like Nmap relies on fingerprinting techniques, which analyze response characteristics (e.g., TCP/IP stack behavior).
The scan cannot gather one or more fingerprints from the target (Option D):
If the system is configured to block ICMP responses, or if certain ports are closed, fingerprinting fails.
Some modern firewalls and intrusion prevention systems (IPS) interfere with OS fingerprinting by modifying packet responses.
[Reference: CompTIA PenTest+ PT0-003 Official Study Guide - "Network Scanning and Fingerprinting Challenges", Incorrect options:, Option A (Firewall block rule): A firewall may block the scan, but typically it would result in no response rather than an "OS identification failed" message., Option B (Outdated scanner database): While an outdated database might miss vulnerabilities, it does not directly cause OS detection failure., Option C (False positive): A false positive refers to incorrect detection, but this is an OS detection failure, not a misidentified OS., ]
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