Google's SafeSearch porn filter was found to exclude non-porn sites such as the American Library Association, in a recent test conducted by the Harvard Law School's Berkman Center for Internet & Society.
Google admits the porn filter isn't perfect but says the test wasn't perfect, either. The porn filter, when engaged, automatically excludes any sites Google only knows about through link analysis, rather than by actually visiting the site.
For example, if a site has banned Google and other search engines from spidering it, Google might still return a link because it sees links to that site on other pages. However, since it hasn't actually crawled the site itself, Google excludes the site when SafeSearch is switched on, because it doesn't know if porn content might be present or not. More discussion of this from Google, as well as comments on the report from search engine marketers, can be found in a recent WebmasterWorld.com thread on the issue.
Sadly, the Harvard report didn't compare Google's filtering to that done by other search engines. Google might be performing better or worse than its competitors, but that's not covered.
The focus is also primarily on how non-porn sites might get accidentally blocked, rather than a look at how well the porn filter works to keep out explicit content. This is addressed rather briefly, to say mainly that even when the porn filter is engaged, it isn't 100 percent successful.
Overall, the porn filter comes off sounding like a terrible thing to use. However, some real world perspective is in order. I remember writing about the first porn filters for crawlers back in 1998. They weren't perfect, but many readers were happy to have them. My article from that time started out with an example of a teacher who did a search for something innocent only to get porn sites showing up in front of her entire classroom.
Flash forward to today, and search for "dolls for girls" on Google without the porn filter. Among the top listings is "Blood Dolls: Gothic Girls in erotic, nude, & fetish photos." That's not something you may wish your seven year old daughter to see. With SafeSearch's "strict filtering" switched on, the site disappears (strict filtering means filtering of both web and image results. By default, "moderate" image filtering is always on).
As I said back in 1998, if you are trying to do proper research and are afraid the results might bring up porn, push the kids out of the room and don't engage any search engine's porn filter. However, if you must search with them present and want some protection, the porn filters will give you some options. But as the latest findings from Harvard aptly point out, the trade-off is that some important non-porn sites might get accidentally filtered.
For more help, Search Engine Watch maintains a list of kid-friendly search engines, as well as a guide to engaging porn filters at search engines. Chris Sherman has given this information a quick update, and he's also currently in the process of a planned look at child-safe searching for a future edition of SearchDay .
NOTE: Article links often change. In case of a bad link, use the publication's search facility, which most have, and search for the headline.