I’ve always loved CGI proxies because they have to deal with all the same problems that every other application has to deal with plus they have to try to force anything and everything that connects back to the remote machine into their pipe to proxy it. Alas, it’s just not that easy. HideMyBrowsing.com is designed to protect users from being seen by content filters. Firstly, how long will it take for content filters to block them? But even if you put that aside, and the obvious using their services to do malicious PHP injection, etc… they are still vulnerable.
I’m sure it’s vulnerable to other vectors as well, that was just the first one I tried. So while interesting and vaguely clever usage of CGI, I wouldn’t use this if you could get fired for looking at porn at work.