ALF article

The article on Application Layer Filtering (ALF) that I wrote for Windowsecurity.com has just been reprinted by SecurityProNews over at http://securitypronews.com/2004/0505.html. There is a lot of interest in ALF these days, and no wonder -- the ability to filter at the application layer not only helps prevent attacks that exploit application layer protocols, but is also a key element in filtering for spam at the firewall, which takes some of the load off your mail server or spam filtering server (of course, you have to be very careful about how you configure content filtering for spam at the firewall, to reduce the possibility of false positives. The most effective spam filtering methods use a multi-layered approach).