If you need to block certain sites from being accessible via a web browser here’s a quick solution.

1. Click Start -> Run
2. Type or Copy the following into the run box-> %SYSTEMROOT%\system32\drivers\etc
   
3. Press Enter -> The Windows Explorer will Open -> Look for the Hosts file
   
4. Open the Hosts file into Notepad (You can do this by dragging the Hosts file into an open Notepad window)
5. You should see something that looks like this:
6. Add a couple of new lines after the “localhost’. For example, If you want to block google.com from loading -> See Image
7. As you can see by the modified Hosts file. I’ve added a couple of new lines. What you are seeing here is the Hosts file re-directing a call to google.com to 127.0.0.1 (this is a loopback IP address in your PC and not an external address) -> This will generate an error page similar to this on your browser when you attempt to surf to google:
   
8. Remember click File -> Save to update your Hosts file after modifying it. Also, you may need to close and relaunch the browser each time you make modifications to the Hosts file.
9. Remember to delete these entries if you wish to unblock those sites. enjoy!