1. A network authentication system for authenticating a network data communication device being used by a user having a network account, the system comprising: a network communication interface configured to electronically receive from the network data communication device: user information identifying the user; security information that the user has entered into the network data communication device; and device information identifying the network data communication device; and a data processing system configured to electronically authenticate the network data communication device if and only if: the user information and the security information match user information and related security information in a user-security information database; the device information matches device information in a device information database; and the network account of the user is indicated as being active in a network account database.