In summary, a vulnerability scanner such as Nessus* or Nmap* is necessary to discover vulnerabilities by internal scans performed by your company or by 3rd parties. Manual Penetration Testing goes quite a bit farther, verifying false positives and manually attempting to show proof of concept for exploits. Something a scanner is not able to do at the present moment.
*Nessus is one of the most popular vulnerability scanners, with over two million downloads across the globe. Additionally, Nessus provides comprehensive coverage, scanning for over 59,000 CVEs.
*Nmap Port Scanner. This tool does not go as broad in its detection but focuses more on mapping open ports (services) across a network. An available port that should not be accessible can still be a vulnerability.
There are many other Penetration Testing Tools; view more info here.
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