A mobile data storage device connectable to an electronic device includes a communication interface unit, a storage module and a control module connected to aforementioned components. The control module allows establishment of a data connection to the electronic device after it is determined that credential information obtained from the electronic device is authenticated, receives an asserted user ID and an asserted user password from the electronic device, looks up a user authority in a permissions table based on the asserted user ID, and enables the electronic device to operate the storage module based on the user authority, the asserted user ID, the asserted user password and a ID-password table.