A method and system for protecting portable computer data from unauthorized transfer or using portable computers to download unauthorized data. The invention is applicable to any computer capable of transferring data, but in one embodiment a portable computer is described. Authorization is enabled by an interface permitting synchronization of the portable computer with a host computer by authentication of the particular portable computer identity. For instance, in one embodiment, when a portable computer is docked with a compatible interface connected to a host desktop computer, it is sensed and identified by the interface. If the particular portable computer identity is authenticated as authorized for that desktop, then synchronization will be enabled by the interface. The computers may then transfer data. However, if the identity is not an authorized one, then authentication will not occur, synchronization is correspondingly disabled, and data transfer is prevented. Various systems can enable the identity authentication.