Today, many airlines, such as Delta, US Airways, Lufthansa and Air Canada are offering Wi-Fi services that allow you to connect to the Internet while you are in-flight. Before flying, it is best to check with your airline carrier to see if they are offering this service. Regarding the security of in-flight Wi-Fi, keep in mind that the Wi-Fi on planes is similar to any other public Wi-Fi hotspot. To ensure security, use a virtual private network (VPN) technology that establishes a secure, encrypted link from your laptop to your remote server.
See also, Is there any way to be safe using a public wi-fi?