An apparatus and method for protecting a content item such as a digitally encoded movie, an electronic programming guide, or the like, by reordering blocks of the content item prior to transmitting it to a receiving device. The receiving device constructs a block reordering structure which is used to access the reordered content item, to facilitate retrieval of a desired block from the original content item. The reordering may be done responsive to an identifier value of the receiving device, such as a serial number.