it's simpel step for beginer to improve their mybb security from hacker
Find file config.php
in folder root/inc/
$config['admin_dir'] = '[color=#ff3333]admin[/color]';
change 'admin' with the name folder you want ex: xytxt
next go to your public directory hosting and rename the directory 'admin' use what you want. ex:xytxt (must same w/ $config['admin_dir'] =)
when you wan to install some plugin, you must remane admin directory (in the plugin package) before you copy to your public directory inside package.
sorry if my english bad..