The stand-out choice in this category is K9 Web Protection by Blue Coat Systems. It's a web based service that uses a special driver installed on your PC to redirect all your browsing through K9's servers, where it is filtered for content. This means that the filtering works with any browser installed on your PC.

The actual filtering itself is highly customizable from a password protected control panel at K9's web site, which offers more than 15 selectable categories, plus the ability to restrict or permit individual sites. Full reports on sites visited are also available from the control panel.

The filtering seems quite accurate; in one hour of browsing, I found only one site which I felt should not have been blocked. I also liked the optional blocking of Spyware and Adware sites. I tried, but failed, to cripple the filter in a few of the obvious ways, such as uninstalling the product or disabling the driver. That fact should be comforting to parents. I suspect, though, that a determined tech-savvy teenager might eventually find a solution. The only real downside was that my browsing speed was slightly compromised as a result of being re-routed through the K9 servers. This will likely be of concern to dial-up users only.

If that's you then you might like to try Naomi, which has the advantage of filtering locally. In my tests it caught all the offensive sites I tried, though occasionally it caught an innocent site as well.

Like K9, it's also difficult to disable. As with K9 I tried the obvious tricks of defeating the filter by terminating the Naomi service and deleting the autostart entry, all without success. Naomi also works with any browser on your system, not just Internet Explorer.

On the downside, it filters by terminating the browser session without warning whenever a banned site is encountered. I found this to be a real annoyance, especially when I had several browser tabs open and lost them all. Naomi is certainly a very capable parental filter but, on balance I preferred K9's smarter logic, greater configurability and friendlier behavior. Modem users will, however, appreciate Naomi’s speed advantage.