You may have for example disabled the ftp server, but still have the command itself installed for using ftp to downloading or uploading to another server.
It is best to test things out on another computer using tools such as nmap and nessus. Nmap is a network scanner which scans for open ports. Nessus is a server/client system that uses nmap and performs more analysis such as whether a version of ssh needs to be upgraded.
Here is the sourceforge site for Nessus: http://freshmeat.net/projects/nessus/
Although you may have the package already.
Also, any command like ckconfig that lists which services are running will also help.
Also check your firewall settings, and use the "find" command to locate all "suid" programs.