I started getting this a while ago when Windows 10 Defender got updated.

As a result, it "undos" changes made by Spybot and Anti-Beacon to my Hosts file.

My solution was to tell Defender to simply exclude the Hosts file from its scan. Problem fixed.

1. Go to: Windows Security -> Virus & threat protection
2. Click on: Manage settings found under Virus & threat protection settings
3. Click on: Add or Remove exclusions found under Exclusions
4. Click on: Add an Exclusion
5. Enter the full path to your hosts file (c:\windows\system32\drivers\etc\hosts)