Ans: This happens when you have Norton antivirus installed in the system and using its web app extension Norton safe web on your browser.
You can mark your site secure for it by following the below steps:
1. Open the Norton anti-virus product, click the "Family" icon and log in to the Supervisor account using your Norton ID and password.
2. Click "Settings" and then click the "Child" picture icon.
3. Click "Web" in the left pane and then click "Specific Web Sites to Allow."
4. Enter the URL of the website you want to unblock in the "Enter a Web Site" field.
5. Click "Add to List" and then click "OK" to unblock the website.
Similarly, you can also block the website. Below is a third-party article which explains it: