Information Post on FTP, Active, Passive settings and SSL by Alun Jones
I started hanging out in the newsgroups again, along with the forums at http://forums.iis.net I ran across a particular interesting post by Alun Jones (Security MVP and maker of WSFTPD). There are a fair amount of posts on http://forums.iis.net about FTP, some are confused by Active, Passive, and SSL settings. His posting in the newsgroups described this very clearly. (IMO). What people are confused about is how Active, Passive connections are handled.
Here is his post
Here is an article series Alun is posting on his blog.
http://msmvps.com/blogs/alunj/archive/2009/07/08/1698917.aspx
Hopes this helps. Thanks Alun for posting such great information!
Steve Schofield
Microsoft MVP - IIS