How do I block HTTP traffic to a single file address, not the entire domain, without a browser-specific program?

Solution 1:

Browsers are for humans, not for software - Minecraft doesn't "use a browser", but it doesn't mean it works in a different way. Actually, it's using exactly the same protocol that browsers do: HTTP.

I have two ideas on blocking that file. Both should work, but both will have some side effects.

1. Block port 80 in your firewall. This is not a good idea, because it will affect all Java programs, so I'm not going into details. If you want to try it, then you can access Windows Firewall by pressing Win+R and typing wf.msc.

2. Block http://assets.minecraft.net/ system-wide through your hosts file. Open Notepad as Adminstrator (right-click it → Open as Administrator), click File → Open and type C:\Windows\System32\drivers\etc\hosts. Open the file and add following line at the end:

   127.0.0.1 assets.minecraft.net
   

   This one has some unpleasant side effects too: none of your programs will be able to connect to that address for any purpose.