Open proxies of various kinds are used nowadays for various evil things like sending mass spam, hacking into your machine, making denial of service attacks (DoS) and the like. Every such machine should be either secured properly or turned off permanently, but that's not an option, since in most cases there is either no administrator of such machines exists at all, or he has no clue about what's on that machine, or it's irrelevant for him. So the only way to stop massive abuse made via such machines is to block them. Also, network administrators (of an ISP for example) are able to warn their clients whenever they are running an insecure proxy services - periodical scanning of client's network may also be a good idea.
This command-line tool, proxycheck, may be used for such purpose. Currently, it understands 3 types of proxy servers: HTTP proxies that allows you to CONNECT to any host:port, SOCKS v4 and v5 proxies, wingate "telnet" proxy servers of various kinds (incl. e.g. CCProxy variants and others), and FTP proxies that are able to create transparent connections.
Continue Reading... This command-line tool, proxycheck, may be used for such purpose. Currently, it understands 3 types of proxy servers: HTTP proxies that allows you to CONNECT to any host:port, SOCKS v4 and v5 proxies, wingate "telnet" proxy servers of various kinds (incl. e.g. CCProxy variants and others), and FTP proxies that are able to create transparent connections.
source:http://linuxpoison.blogspot.com/2011/04/135781677518222.html