A report by Harvard Law School's Berkman Center for Internet & Society stated that SafeSearch excluded many innocuous websites from search-result listings, including ones created by the White House, IBM, the American Library Association and Liz Claiborne.[7] On the other hand, many pornographic images slip through the filter, even when "innocent" search terms are entered. Blacklisting certain search terms is hindered by homographs (e.g., "beaver"),[8] blacklisting certain URLs is rendered ineffective by the changing URLs of porn sites, and software to tag images with copious amounts of flesh tones as pornographic content is problematic because there are a variety of skin tones and pictures of babies tend to have a lot of flesh tones.[9] Google's ability to filter porn has been an important factor in its relationship with the People's Republic of China.[10]