An audio and/or video content receiver configured to receive encoded audio and/or video access-controlled content from a content source, the content receiver comprising: a host module; and a conditional access module (30, 50) having an access control unit for processing access-controlled content to generate non-access-controlled content, the host module and the CAM being arranged to provide an encrypted transport stream link (16, 21, 35, 33, 22, 13) for communication of the non-access-controlled content between the CAM and the host module; in which: the CAM comprises an identification data module configured to apply a digital watermark to decoded audio and/or video non-access-controlled content to generate marked decoded audio and/or video non-access-controlled content; the CAM is configured to communicate, via the encrypted transport stream link, encoded audio and/or video non-access-controlled content to the host module; the host module comprises a content decoder to decode the encoded audio and/or video non-access-controlled content to generate decoded audio and/or video non-access-controlled content the CAM is configured to receive a control message, from the content source, indicating whether some or all of the audio and/or video access-controlled content should be processed by the identification data module to apply the digital watermark; in response to receiving the control message, the CAM is configured to request at least some of the decoded audio and/or video non-access-controlled content from the host module for processing by the identification data module; the host module is configured to communicate, via the encrypted transport stream link, the at least some of the decoded audio and/or video non-access-controlled content to the CAM for application of the digital watermark by the identification data module; and the CAM is configured to communicate the marked decoded audio and/or video non-access-controlled content to the host module via the encrypted transport stream link. a host module; and a conditional access module (30, 50) having an access control unit for processing access-controlled content to generate non-access-controlled content, the host module and the CAM being arranged to provide an encrypted transport stream link (16, 21, 35, 33, 22, 13) for communication of the non-access-controlled content between the CAM and the host module; in which: the CAM comprises an identification data module configured to apply a digital watermark to decoded audio and/or video non-access-controlled content to generate marked decoded audio and/or video non-access-controlled content; the CAM is configured to communicate, via the encrypted transport stream link, encoded audio and/or video non-access-controlled content to the host module; the host module comprises a content decoder to decode the encoded audio and/or video non-access-controlled content to generate decoded audio and/or video non-access-controlled content the CAM is configured to receive a control message, from the content source, indicating whether some or all of the audio and/or video access-controlled content should be processed by the identification data module to apply the digital watermark; in response to receiving the control message, the CAM is configured to request at least some of the decoded audio and/or video non-access-controlled content from the host module for processing by the identification data module; the host module is configured to communicate, via the encrypted transport stream link, the at least some of the decoded audio and/or video non-access-controlled content to the CAM for application of the digital watermark by the identification data module; and the CAM is configured to communicate the marked decoded audio and/or video non-access-controlled content to the host module via the encrypted transport stream link. the CAM comprises an identification data module configured to apply a digital watermark to decoded audio and/or video non-access-controlled content to generate marked decoded audio and/or video non-access-controlled content; the CAM is configured to communicate, via the encrypted transport stream link, encoded audio and/or video non-access-controlled content to the host module; the host module comprises a content decoder to decode the encoded audio and/or video non-access-controlled content to generate decoded audio and/or video non-access-controlled content the CAM is configured to receive a control message, from the content source, indicating whether some or all of the audio and/or video access-controlled content should be processed by the identification data module to apply the digital watermark; in response to receiving the control message, the CAM is configured to request at least some of the decoded audio and/or video non-access-controlled content from the host module for processing by the identification data module; the host module is configured to communicate, via the encrypted transport stream link, the at least some of the decoded audio and/or video non-access-controlled content to the CAM for application of the digital watermark by the identification data module; and the CAM is configured to communicate the marked decoded audio and/or video non-access-controlled content to the host module via the encrypted transport stream link.