Hello Kathy. HTML files in themselves aren’t malicious, what malformed HTML files do is redirect a user to a fake/malicious website that. Most times looks to be legitimate. The malware is then installed when the user has been redirected to that site. The malware will then look for ways to install itself using unpatched vulnerabilities in the OS or the browser being used. At times there are vulnerabilities known a zero-days and commonly these issues we don’t know about them until a specific time has passed allowing the OEM to fix the issue with patches.
Version 24.xx has for me nailed a website once that attempted 153 connections, all instances show in my Norton history as such. You may be seeing a malicious file quarantined and, it may be resident with more detections.
My suggestions are Download RKill and run it to detect malicious processes running and have it stop them.
Next, download Malwarebytes
and run a full scan to see what, if anything it detects.
As a test at this site: Ecar . org which tests anti-viral software for detection of viruses. This is NOT a virus but will act as one for testing purposes. Norton version 24.xx is doing its job. Your file may have already been on your computer sitting in a temp folder before version 24.xx came along. I am using the Opera GX Chromium based browser on Windows 10 Professional x 64.