Abstract: An integrated circuit comprises an identification portion having an output representative of one or more bits of digital information identifying the integrated circuit. This identification information may, for example, allow the manufacturer to determine which photolithographic masks were used to manufacture the integrated circuit. The identification portion is formed at least partially by a plurality of metal levels. Modifications to the integrated circuit's identification information are facilitated by designing the identification portion such that its output can be changed by modifying any one metal level among the plurality of metal levels that form it.