A digital publishing firm in Charlotte, North Carolina, noticed suspicious probing activity against its public...

The correct answer is D. Nikto.

Nikto is an open-source web server vulnerability scanner. It is specifically designed to scan web servers for dangerous files, outdated server versions, version-specific problems, configuration issues, and known web server weaknesses.

CEH-aligned web server hacking material states that Nikto scans for potentially dangerous files and programs, checks for outdated server versions, and identifies version-specific problems across various servers . Another CEH exam reference describes Nikto as a web-server-focused vulnerability scanner that checks for file problems, script errors, and server configuration errors .

Option A. Nessus is incorrect because Nessus is a broad vulnerability scanner, not the most specific match for the web-server-focused checks described.

Option B. OpenVAS is incorrect because OpenVAS is also a general vulnerability assessment platform.

Option C. Qualys VM is incorrect because Qualys VM is an enterprise vulnerability management platform, not the specific web server scanner described.

Option D. Nikto is correct because the described capabilities directly match Nikto.

Therefore, the best answer is D. Nikto.