Program code in a Web page hosted by a server and/or in server side code executed by the server is specially configured so that a modified media file whose source is embedded in the Web page and which is streamed by the server is properly playable only in browsers of media devices accessing the Web page. Thus, if a copy of the modified media file is downloaded to the media device or otherwise procured, the user of the media device is unable to properly play the downloaded copy by using a conventional media player. Further, if the downloaded copy is shared on a file sharing network, users of the file sharing network that download copies from the media device are also unable to properly play their downloaded copies by using conventional media players.