Benign Feature, Malicious Use
An interesting and unknown feature used by sysadmins around the world in some large corporate networks is the use of proxy-auto config (pac) files. This benign feature is accepted by all modern browsers and is described in detail here. It contains a function to redirect your connection to a specific proxy server. Unfortunately this simple and smart proxy technique are being largely used by brazilian malware writers to redirect infected users to malicious hosts serving phishing pages of financial institutions. A .pac script URL is configured in the browser, in the field “Use automatic configuration script”: ...