I'm playing Minecraft over Hamachi with some friends. One of them said he could make himself op on MY server with a program called Modio. What is this, should I be worried, and what can I do against it?
I'm not entirely sure what Modio has to do with Minecraft. It seems to be a utility that can transfer game saves between a PC and an Xbox 360.
If you are indeed running a server without name verification, you should worry anyway, if anyone on your server is an operator. Setting
false causes the server not to verify usernames with minecraft.net, which allows anyone to log in with any handle they wish. If you have given someone else or yourself operator privileges, this person could hijack the nickname of an op and thus gain their status.
If you want to defend yourself against this, your options are: