I had a chat with a colleague today regarding FTP access. For some reason, it made me think of the /etc/shells file. This file allows an FTP user access to the system if his/her shell is defined in it. An example is shown below.
By the way, this is a user created file. #cat > /etc/shells /sbin/sh /bin/sh /bin/csh /bin/ksh /bin/bash /bin/tcsh control ^d