A method of encoding a message into a document containing known information is disclosed. The method comprises identifying (1502) a plurality of logical information content categories associated with the known information, establishing (1503) a priority order in which said message is to be added to each of the categories, determining (1504) an amount of said message to be added to each of the categories, and encoding (1506) the message into the document according to the established priority order and the determined amount.