How to fix ERR_NAME_NOT_RESOLVED (Windows, Mac OS, Android, iOS) (Mac OS)

The hosts file enables you to add URLs of webpages you want to block, which will automatically be blocked in every single browser installed in your computer. Also, some viruses can modify the hosts file in order to prevent you from downloading an antivirus software which can find and remove the virus.
 
All you have to do to fix this issue is to open and modify the hosts file. To modify the hosts file:

1.  Open the Terminal.app by going into Applications -> Utilities -> Terminal.
   
   
2. Type the following line: sudo nano /private/etc/hosts (type your username and password when asked)
   
   
3. If you notice a URL of a websites you visit, or websites of antivirus software, delete them and press and hold Control + O to save the changes and Control + X to exit
   
   
4. Flush the DNS cache by entering the following line (depending on your OS version):
   
   
   • dscacheutil -flushcache - Mac OS X Snow Leopard (v10.6 through v10.6.8)
     
     
   • sudo killall -HUP mDNSResponder - Mac OS X Mavericks, Mountain Lion, and Lion (v10.9.5 and earlier)
     
     
   • sudo discoveryutil mdnsflushcache - Mac OS X Yosemite and later (v10.10 through v10.10.3)
     
     
   • sudo killall -HUP mDNSResponder - Mac OS X Yosemite and later (v10.10.4 or later)