MBP Retina, 13-inch, Late 2012, with MacOS 10.13.5 What's Web Sharing and why incoming connection to it are blocked and mark as severe security risk by Norton?
Web Sharing, also known as Internet Sharing, allows you to share your Mac's internet connection with other computers.  It can also provide you with the ability to share web pages from your Mac.

This could be considered a security risk by many security software applications because if it's not configured correctly, you could allow others to access to your computer.  I will not go into details about the pros &amp; cons about that here because it's outside the scope of your question.  

If you don't have a reason to share your connection or deliver web pages, you disable this feature from within System Preferences.  I'm assuming you're using macOS v10.14.2.


Open System Preferences.
While it's open, go to the View -&gt; Sharing menu item.  This will bring-up the Sharing preferences.
Uncheck Internet sharing