It is possible to bypass the Fortinet anti-virus engine when sending files over FTP under certain conditions. Those conditions will be disclosed later since Fortinet has not fixed the problem yet. This bug was tested on FortiOS v2.8MR10 and v3beta.
You can download this advisory from the following link: https://packetstormsecurity.com/files/download/43759/Fortinet-ftp.txt
Source: https://packetstormsecurity.com/files/43759/Fortinet-ftp.txt.html