[1] The system works by applying a bogus data track onto the disc during glass master manufacturing.
Since additional data sessions are used, the CD is not Red Book compliant and should not use the "Compact Disc" logo.
DVD players and car stereo systems seem to have most problems[citation needed] with incompatibilities of key2Audio protected CDs.
A protected CD still achieves a maximum recording time of 77 minutes and supports full ISRC, UPC and CD-Text capabilities.
Early versions of this copy protection were infamous for being easily circumvented with a marker pen, by drawing a circle on the rim of the visible edge of audio data.
For this purpose, the user interface for key2Audio on PC allows for navigation and includes a copying and burning tool, as well as additional content such as bonus pictures and lyrics.