Hi, in my server, I have offline mode to true and I have some hacker who come with Ghost (like Huzuni) and I can use ./bminfo or /ban or other with this player (juste ./seen to get the IP and i can /ban IP), It create an error in database with this name and if this same name come with vanilla version, I can't use ./bminfo or other. I want to ban or just block Ghost Client to come to my server, can you help me ?

I'm sorry for my bad english, I'm not english :/

Offline mode is not officially supported. If you run into trouble you are on your own.

The "error" might be interesting though. Where is it?
Check your console output.

I don't have error with ./bminfo just don't find the pseudo.

As stated at #610 offline mode support has known flaws with case sensitivity. Though it was a contribution and will not be enhanced by BM itself. Feel free to enhance offline mode support by yourself and provide a PR.