SSH users have acess to the hole server

Hi.

Then I should help one that is hosted on my server, I have to login via ssh. That I do a lot. But with his username and password, and with his password I edited in a file under /etc.

Wops..

I have tried with many username - and all have acess to the hole server.

PLEASE FIX IT.

Meanwile I have uncheck all users for ssh