Flash Media Server administrator password visible in FMS.INI
The user name and password you see in the FMS.INI file are only the initial settings used when FMS is installed. Actual users and passwords are stored in the USERS.XML file that is in the same location as FMS.INI.
To set a secure password on the admin account, open the Adobe Flash Media Server (FMS)Administration application. Select the "Manage Users" pane and then change the password on the admin account. (You can change it to the same thing if you like.) The password goes into USERS.XML and is encrypted.
The admin user in FMS.INI is used only to log in to the admin interface. The FMS service itself uses a different password. By default, they both (the Admin FMS and the normal FMS) are set to log in as Local System. If they never require access to network resources, then it's unnecessary to change it. And you'd do that just like you would for any other Windows service.
When you add more users to log in to the FMS Admin application itself, they make entries only in USERS.XML, not FMS.INI.