A method and apparatus to identify user who purchased/downloaded audio/video content. When an audio/video content is purchased/downloaded the content is encrypted for the user and a unique identification code is added as part of the purchase/download. When the encrypted content is decrypted and assembled the identification code is converted to a spatial or time domain vector and added to the original content. The identification code can be split into individual digits/bytes to represent in spatial or time domain vector. The identification code can be visible or invisible. By examining the encoded original content, the user who purchased/downloaded the content can be identified from the unique identification code.