Hello Ginery,
Thank you for posting your query on Microsoft Community Forum.
I would appreciate if you can provide us the following information to help us understand the issue better.
- Could you please provide names of some websites which are getting blocked?
- Have you tried to open those websites from any other browsers? If yes was the result same?
- How are you sure that these websites are getting blocked by Defender?
As per your issue description it seems that you are unable to open some websites then, there might be a chance that the website is not compatible to Internet Explorer 11. So I would suggest you to open those websites in compatibility view and see if it helps.
- Open Internet Explorer 11.
- Open website which is getting blocked.
- Press alt key to open tool bar.
- Now click on tools.
- Then click on Compatibility view settings.
- You will see the name of websiteunder Add this website, so click on add to add this website.
- Close the window and restart your computer.
If issue still persists you may try to trust those websites by following the steps mentioned below.
Step 1: Open the trusted sites
- Open Internet Explorer.
- Press the Alt key to make the tools menu visible.
- In the menu, click Tools.
- Now click Internet Options.
- Go to the Security tab.
- Select Trusted sites.
- Click Sites**.**

Step 2:
Add the trusted website
- Enter the address of the website you would like to add.
- Click Add.
- Close the opened Trusted Sitesand Internet Options windows.

Hope this would help. If issue still persists post back with current status of your computer and result of the proposed suggestion, we will be happy to assist you.
Thank you.