A method for delivering digital data to a plurality of processing units is disclosed. A plurality of portable memory device containing a first set of digital data is distributed to the plurality of processing units. The first set of digital data is unencrypted and comprises a content portion and an identification label. At least one of the processing units sends the identification label to a remote station. The remote station then encrypts a second set of digital data and delivers the encrypted data to the requesting processing unit. The requesting processing unit can decrypt the encrypted data, and combine the decrypted second set of data with the content portion.