I'm looking for a FTP backup script which can be ran from the backup server, but nor from your local server. The reason is obvious: In case anybody gains root access to the server, he would also have access to the local FTP backup script including login and pasword of the backup server.
Ok, the answer is really firewalls. Set the firewall on your backup server to only allow access to the Server (both in and out). Block everybody else (except of course, your own IP so you can access it).
The backup FTP script is easy to do - I do it on windows, but linux should be similar. Put the FTP commands in a file, and have a script run ftp that loads the file in.
Of course, setting up SSH with a password-less key and using Rsync to copy the files is not as simple, but is more secure and will use less bandwidth.