DansGuardian is a web content filter which currently runs on Linux, FreeBSD, OpenBSD and Solaris. It filters the actual content of pages based on many methods including phrase matching, PICS filtering and URL filtering. It does not purely filter based on a banned list of sites like lesser totally commercial filters.
One approach is client-based softwareproducts which, when loaded onto an individual computer, check specific Web site requests against a database of Web sites deemed inappropriateand disallow the retrieval of the content. There are several drawbacksto client-based products. First, the users must load software onto the individual computer. It is immediately out of date because new objectionable sites appear on the Internet daily. Updates are usually available, but continually updating is troublesome to the user. They are often easy to bypass because they are loaded on the same computer they're protecting.
The approach we chose to use is server-based
filtering which resides at the network level, so that each computer does
not have to have software loaded. In our case, we have the filtering server
hosted at our network and then we allow our subscriber access to it. This
is the most practical approach, users automatically receive the most updated
list of blocked sites daily.