One quite basic difficulty, one shared with end-user filtering methods as well, arises from the fact that proxy servers typically work by possessing lists of URLs of Web sites to which they will not grant access because the content at the sites is harmful or illegal.
与用户过滤方法一样，一个相当基本的问题是代理服务器运行必须拥有因内容有害或非法而不允许进入的网站的URL清单。