If the user is logged in, then the image file loads successfully, which causes the executions of loggedIn. If the user is not logged in, then notLoggedIn is executed. The result is an ability to test easily and invisibly whether a visitor is logged in to a particular Web site that a Web developer does not have a relationship with. This login-detection technique, which leverages CSRF, can be applied to online banks, social networks, Web mail, and basically anything else useful to an attacker. The attacker behind http://coolwebsite/ just has to find the URLs that respond in a Boolean state with respect to login.

via The Web Won’t Be Safe or Secure until We Break It – ACM Queue.

Browser intranet hacking allows Web-site owners to access the private networks of their visitors, which are probably behind network firewalls, by using their browsers as a launch point. This attack technique is painfully simple and works equally well on enterprises and home users, exposing a whole new realm of data.