What you are doing when you do that, is creating a small Wi-Fi network using your AirPort card. Anyone withing range can share this connection. I have done this a couple of times on vacation - plug my BlackBook into the ethernet and share the connection with the kids ( can't go a single day w/o Facebook) and their MacBooks. Worked with my 12"PB also. not a lot of range so I would not worry too much about security.