I've set Minecraft up with my account on a Windows guest user for my little siblings to play singleplayer. For security reasons, as well as concerns for the children themselves, I'd like to disable multiplayer on that account by forcing the "Play Offline" mode.
New versions will be added by me, manually, along with OptiFine and whatever other mods were necessary.
I'm thinking that the best way to do this would be related to destroying or invalidating the login token for that user, but how can I do this without making it re-request the password?
Best Answer
Alas, "Online mode" refers only to the account validation. You can still log into servers just fine if they don't enforce it.
What you can do, however, is simply to go to your firewall settings and disable Minecraft's traffic rules. Then it will indeed be unable to contact anything through IP.