Our school currently relies on Sonicwall's Content Filtering Service to block offensive and malicious websites. We used iPrism with good results a few years ago, but they began raising their prices substantially, so we reverted to the Sonicwall CFS, for which we were already paying.
I know that no filter is 100%, but we had some pornography get through the other day, I think in the form of an advertisement shown during a Bing video search. I wasn't able to reproduce this, so can't confirm 100%. I've used the free MVPS.org DNS solution at home with good ad blocking results, but I'm not sure if that would be good to implement network-wide. I'm also looking at some browser plug-ins(most users use FF), but I would have to implement them for all browsers or restrict the allowed browsers(we allow IE, FF, Chrome). I'm looking for a free solution to this first, and there seems to be a lot of options. Any suggestions? Thanks, Mike
