The first step to add filtering for an FTP servere is to add antivirus filtering.
We will need to modify the setup procedure a bit to apply the appropriate patches :
So, download the patch source
wget http://www.thrallingpenguin.com/resources/mod_clamav-0.7.tar.gz
tar xzvf mod_clamav-0.7.tar.gz
cp mod_clamav-0.7/mod_clamav.* proftpd-1.3.1/contrib
Apply the required patch:
cd proftpd-1.3.1
patch -p1 < ../mod_clamav-0.7/proftpd.patch
