An article on an Arizona news site suggests that drive-by hackers are worrying residents in an upscale area of Scottsdale. The article is nothing more than FUD, or at least it should be.
If these users are really worried about these war-drivers accessing their networks then they should enable the highest level of security supported by their wireless devices.
For most people today that will be WPA (though even static WEP is better than nothing at all – and only a really determined war-driver will waste the time trying to crack the encryption on an unknown person’s network). Very soon people will be able to enable WPA2, with very secure AES encryption.
As for credit card numbers, nobody should be posting these online unless the site they are sending them to is already encrypting the link. In which case it does not matter whether the wireless network is encrypted or not – the SSL tunnel between the browser and the remote web site will protect the card details.
Windoze users are probably much more at risk of being attacked through the numerous flaws that it contains than they are from a drive-by “hacker” using their unprotected wireless network.