Jim O'Halloran's Weblog: SquidGaurd and Dan's Guardian - Web Filtering Software is a post on Jim O'Halloran's blog about a couple filtering programs for the Squid web cache.
I wish him luck if he's going to do this sort of thing. Both are a slippery slope into constantly reconfiguring the filters to keep up with the new porn sites added every day.
I've tried keyword filters but that gets out of hand very quickly. Above a certain number of lines (256-character limit), the cache noticably slows.
We then tried various filtering plug-ins, like Squidguard, but they too slowed service once a certain number of sites were entered.
About the only way we were able to get above 5000 sites was to reconfigure Squid to use a private DNS server (only for the cache, but not on the cache) and set up a poison DNS zone for each porn site domain. We were up to well over 21,000 porn sites before we quit adding them (it was turning into a full time job).
The programs DO work, just not well under heavy loads. And there's always a new porn site that's not on the list. I'll post a howto here in the next few days for anyone that actually cares to read it.
Legislating the use of content filtering, while meaning well, is only going to expose various institutions to litigation. Anyone capable of using Google's extra features can get around filters very easily. Some soccer mom is going to sue a city library because her kid saw someone else's kid viewing porn in the back row of workstations at the library. I wish legislators would realize that a public library is an adult building, similar to a church or courthouse. In those areas, children are supposed to be supervised. A public library is no different.