If the user is connected to an unencrypted wireless network or the encryption is weak (WEP), display either a warning symbol on the network icon or display a warning message (popup/slidein).
Make this information available using dbus for other applications(online banking).Using this information they can stop the user from doing anything dangerous like banking over an unencrypted and open connection.
If your online banking is not encrypted by SSL, then the lack of encrypted wireless should be the least of your worries. And if it is, then it's perfectly safe to do over unencrypted wireless anyway. -1