This script will add rudimentary logging to the FTP server.
The logfiles can be read with your webbrowser:
http://qnap/ftplogs

You can change the type of logging to anything you would like.
More information on the proftpd website:
http://www.proftpd.org/

This script is included in custom.tar [10 KB] see the startpage, it is located in custom/scripts/

The script should be run:
1) on every reboot (automated by adding the script to /share/MD0_DATA/custom/autorunmaster.sh)
2) after changes have been made to the ftp settings or shares have been added

You can also run the proftpd.sh script separately: /share/MD0_DATA/custom/scripts/proftpd.sh
Original configfiles can be found in /share/MD0_DATA/custom/config-backup

.htaccess
To be able to see the files with your browser in http://qnap/ftplogs, you will also need the htaccess.sh script.
After installing and running the htaccess.sh script you have to create a .htaccess file in /share/MD0_DATA/Qweb/ftplogs:

cd /share/MD0_DATA/Qweb/ftplogs
echo "Options Indexes" > .htaccess

Please note:
This script only works with older versions of the firmware.
Newer versions have logging built in, you can find it in the menu 'System Logs' under 'System Connection Logs'.