A method and system to maintain portable computer data secure and an authentication token for use in the system are provided. The present invention provides for fine-grained authentication and full security of a laptop file system. The laptop disk is encrypted and each time data is fetched from the disk the laptop sends a short message requesting a decryption key from an authentication token worn or associated with the proper laptop user. If the user and his/her token are "present," then access is allowed. If the user and his/her token are not "present" (i.e., within a predetermined radius), then access is disallowed and all in-memory data is flushed to the disk. The user wears the small authentication token that communicates with the laptop over a short-range, wireless link. Whenever the laptop needs decryption authority, it acquires it from the token; authority is retained only as long as necessary.