St. Bernard's iPrism appliance is a content and application filter that lives up to its name: Like a prism, it transparently fits into your network and reflects or divides Internet traffic into 60 distinct categories for easy monitoring. It monitors and blocks objectionable Web traffic using a comprehensive URL database of Web sites. Although it does not filter by keywords or phrases, it makes use of complete URL path names, letting you block objectionable subdirectories while allowing access to top-level directories that may be permitted according to your acceptable-use policy. The URL database is updated automatically and reviewed by human editors for accuracy.
IPrism also denies Internet services by IP address and port or by protocol -- FTP, HTTP, ICQ, IMAP, POP3 or telnet, for example. And you can block a custom service based on the same criteria.