Disable Wifi Hotspot Popup Window
While littlerock's answer works, there are better options. Specifically, you can do one of the following. The order is what I would recommend:


Change the system setting. This is preferred, as it's using the OS as designed. Do this on the console and provide your password:

sudo defaults write /Library/Preferences/SystemConfiguration/com.apple.captive.control Active -boolean false
Prevent OSX from detecting the fact that we're on a captive portal, by editing the hosts file. Apple uses their domain to test whether we are on the Internet or not. To do this, edit the following file as root with a text editor:

/etc/hosts

127.0.0.1 captive.apple.com
Last, you can follow littlerock by renaming the following file (as root) to whatever you like:

/System/Library/CoreServices/Captive Network Assistant.app