On Windows XP with Internet Explorer 7 installed several "web related" URI schemes do not launch the registered protocol-handler if the URI contains an invalid %-encoded sequence. This was initially reported by Billy Rios and Nate McFeters with additional investigation by Secunia. A patch that mitigated the known exploits was shipped with Firefox 188.8.131.52 as described at MFSA 2007-27. That mitigation did not prevent the incorrect file-handling programs from launching which left some risk. An additional fix has been applied to Firefox 184.108.40.206 that detects when Windows would mishandle these URIs so that the wrong program does not get launched.