19. The computer-readable medium of claim 18 further comprising: encrypting the content using a third control word that serves as a second encryption/decryption key; assembling a second transport stream that includes the content encrypted using the third control word; transmitting the second transport stream over the content delivery network to a second subscriber terminal; and transmitting the third control word to the second subscriber terminal.
19. The computer-readable medium of claim 18 further comprising: encrypting the content using a third control word that serves as a second encryption/decryption key; assembling a second transport stream that includes the content encrypted using the third control word; transmitting the second transport stream over the content delivery network to a second subscriber terminal; and transmitting the third control word to the second subscriber terminal. 21. The computer-readable medium of claim 19 further comprising selecting the variable control word such that no resulting value for the decryption key is equal to the third control word.