Date: Thu, 23 Jan 1997 14:15:38 -0800 From: Caveh Frank Jalali <caveh@Eng.Sun.COM> Subject: URL filtering, Re: ad.doubleclick.net (RISKS-18.78) The obvious defense against hostile or undesirable web sites is to not visit them in the first place. This process can in fact be automated in netscape's browser. This saves bandwidth and your time! The basic premise is that the browser may optionally execute a function on every URL before it is accessed to determine whether a direct connection should be made or a proxy should be used in the process. This affords the opportunity to [mis]direct the browser to fetch the document from an invalid source. this is a good approximation of not getting the document at all. We sit behind a fire wall, so all WWW access has to funnel through a proxy. If I tell netscape to fetch an external document using a direct connection, the connection attempt will fail, and the document will not be accessed. Netscape will put a broken image icon in its place. Here are the nuts and bolts to do it, but some assembly is required: Under options/network preferences/proxies, select "automatic proxy config" and tell it which file to use. Call it something like "file:///HOMEDIR/.netscape/proxy.pac", replacing HOMEDIR with your home directory; the actual code is included below. Next, go to options/general preferences/helpers and create an application helper of type "application/x-ns-proxy-autoconfig" for suffix "pac", handled by "navigator". Install this java-script code to do the actual filtering. call it "file:///HOMEDIR/.netscape/proxy.pac", as mentioned before. ================ function FindProxyForURL(url, host) { if ( isResolvable(host) && ! shExpMatch(host, "[0-9]*") ) return "DIRECT" ; else if (host == "advertising.quote.com") return "DIRECT" ; else if (host == "ad.doubleclick.net") return "DIRECT" ; else if (shExpMatch(url, "*:*/ads/*")) return "DIRECT" ; else return "PROXY webcache:8080; "; }