Do Not Allow Joomla Extensions To Be Installed For Joomla 1.5 -3.X
When you develop a website and allow a user to have Administrator or Super Administrator privileges, you may want to alter the back end so that Extensions cannot be installed at a later date. You may have various reasons for doing so. For one, an insecure or vulnerable extension can cause problems.
Therefore, not allowing extensions to be installed can remove that threat to the file system. In addition to removing the ability to install extensions, FTP or any other protocol to connect to the host should not be allowed to the client either. Many people do not take security seriously and just see the hosting as a free for all. Then, when something goes wrong, they blame you.
To remove the ability to install extensions ,
1) Open administrator/components/com_installer with FTP >Rename or folder or back it up on another device or path on the server.
To remove the installation from showing up in the menu for Joomla 1.5,
2) Open administrator/modules/mod_menu/helper.php and comment the following line
//$menu->addChild(new JMenuNode(JText::_(‘Install/Uninstall’), ‘index.php?option=com_installer’, ‘class:install’));