The Null Device
Freedom To Tinker has a tutorial on how to create "copy-protected" CDs, describing how the protection works:
Notice that the tracks are grouped into two sessions -- essentially two independent CDs burned onto the same disc. Unprotected CDs that combine audio and data files contain audio tracks in the first session and a single data track in the second. The only difference in the passive protected CD you just created is that the second session contains two tracks instead of one. ... This simple change makes the audio tracks invisible to most music player applications. It's not clear why this works, but the most likely explanation is that the behavior is a quirk in the way the Windows CD audio driver handles discs with multiple sessions.
For an added layer of protection, the extraneous track you added to the disc is only 31 frames long. (A frame is 1/75 of a second.) The CD standard requires that tracks be at least 150 frames long. This non-compliant track length will cause errors if you attempt to duplicate the disc with many CD drives and copying applications.It says that this only works on Windows. I wonder whether this is the same scheme as used by EMI Australia, circa 2004. Their scheme resulted in errors reading the table of contents under Linux, with tracks having anomalous lengths. Strangely enough, it only worked on some drives: a then-recent Pioneer DVD drive choked on it, but an old 24X CD-ROM (borrowed from a beige G3 Macintosh) had no problems.
Despite these limitations, who wouldn't enjoy finding a homemade copy-protected CD in their stocking? They're a great way to spread holiday cheer while preventing anyone else from spreading it further.
(via bOING bOING)