A security system for preventing disc players from being used with unauthorized software is disclosed. The security code is stored through modulating an offset of the physical position of a plurality of data bits from a nominal track position. A two part optical read head provides an RF signal corresponding to the presence of a physical offset modulation. The RF signal is present when there is a physical offset of the data bits defining a first logical state and the absence of the RF signal defines a second logical state. A digital security code is encoded and decoded in this manner. A system for encoding a security code through modulating the physical offset of a plurality of data bits from a nominal track position is also disclosed.