There are no known Windows-like Viruses in the wild that self replicate and affect macOS, because of the underling UNIX Foundation and Permission Limitation.
So with above in-hand, the Norton Software is really only protecting there bank account by offering Zero Protection for a Non Existing issue affecting macOS.
Further, the Norton Software may have done the opposition to Protect and made the computer and High Sierra more vulnerable because the Norton software may have or will interfere with the normal operation of the OS, alter, modify, remove or delete or attempt to do so is an invitation for disaster and may require a Reinstallation of the OS.
As a testament to what this specific software can and does - please read the first 600 posting on the ASC Forums and draw ones own conclusions https://discussions.apple.com/search?q=norton%20anitivi
The The Built in Security is all that is required to protect the computer and some due diligence on the art of the User.