Security Software developer Authentium reports that the wireless network you try to access at the airport may not be legit. As quoted in this article :

Recent tests at Chicago's O'Hare airport revealed that more than 90% of wireless networks available within the passenger terminals were ad-hoc, or peer-to-peer, connections, and more than 80% of these were advertising "free" Wi-Fi access. Many also displayed fake or misleading MAC addresses."

Windows is often configured to connect automatically to a network, so be careful when you're in an unfamiliar area. Before you connect at the airport, make sure the network you're connecting to is a wireless network, not "peer-to-peer" -- your Wireless Network Connection window will indicate the type of network.