Web applications are not protected by todays network level firewalls,
because they allow access to TCP port 80 without restrictions. However, many
successful attacks today are not on the network level, but on application
level. For protecting against application level attacks, a firewall must
understand the application protocols, that are used on its open ports. This
happens in application level firewalls and for Web application in Web
application firewalls. The underlying concepts of Web application firewalls
differ much from the concepts of traditional network level firewalls. This...