"From there, it's sent over an HTTPS connection to your contacts' PC or phone (if they're also on WiFi sense)."
@Kellly: Thank you for explaining the underlying architecture. If that's the level of security that has been built in, then it does seem quite secure. It seems like an efficient way to handle the case where the Wifi key changes and everyone has to update it. As long as they are added to your network, they'd not need to update the key on their ends. Further, if you want to prevent someone from using the Wifi, you can simply remove them from your network