If you download the new version of
Minecraft.msi it will install a minimal working Java in the directory of the Launcher. By default, the game will prefer this to any other java installation.
This means that you can add
[Minecraft]/runtime/jre-ABC/DEF/bin/javaw.exe to the block list of your firewall, instead of blocking the default port (25565).
- Open "Windows Firewall with Advanced Security" as an Administrator
- Click on "Outbound rules" in the left pane
- In the right pane, click "New rule..."
- In the wizard, set it to program and locate the
javaw.exe mentioned above.
- Set it to "Block all connections".
- Optional: Repeat step 2-5 for
javaw.exe affects the game itself. Any attempt to join a server will cause a
java.net.SocketException: Permission denied, even though the launcher won't say "Play Offline".
java.exe will prevent the launcher from accessing
minecraft.net, so you will not be able to install new versions if you simply run
Minecraft_Launcher.exe, which uses the blocked java. You can easily subvert this by running
However, this is not really needed, and a simpler solution is using Windows UAC. Specifically, go to
%appdata%/.minecraft. Right click on
versions > Properties > Security > Edit. Select your kid's account and check "Deny" for "Write". Repeat his for
launcher_profiles.json. This will prevent your kids from downloading new versions, or modifying the existing ones. Furthermore, any changes to profiles with revert once the launcher closes.
A note on security: This method only works as long as the restricted user doesn't know how to run the game using a different java installation.