Verifies authentic copy by checking existence of "twin sectors" which are sectors with same logical address but different data. However, twin sectors may be hard to read in order to copy but are easy to write.
By intentionally violating Red Book CD Digital Audio standards, such as erroneous disc navigation and corrupted data, prevents successful ripping of the data. However, the original copy itself does not play correctly in some CD/DVD players.
Intended to make the CD play only on CD players and not on computers by applying bogus data track onto the disc during manufacturing, which CD players will ignore as non-audio tracks. The system could be disabled by tracing the outer edge of a CD with a felt-tip marker.
Installs software on the computer that tries to play the media so other software cannot read data directly from audio discs in the CD-ROM drive. Silently installing software on a computer created a controversy about modifying a computer's behaviour without a user's consent.
Creates fake scratches on the disk image which copying programs will automatically try to fix. Instead of alerting the user that the copied disc is detected, the program will play the game in buggy manner.
The authority pattern pressed on internal circumference of the media, which could not be copied, is used to detect authorized copies. Some titles also uses Libcrypt mechanism to validate the disc by using checksum as magic number to subroutines.
A map file that contains all of the exact positions and file size info of the disc is stored at a position that is beyond the file limit. The game calls this place directly so that burned copy with no data beyond file limit cannot be played.
Since no blank media or writer exists, the media itself cannot be copied, but one could make ISO image (a file version of the UMD) on a memory card. The unique format also made the media difficult to adapt and expensive.
It has been theorized that the discs have a second partition that is read from the outside in (opposite current standards thus making the second partition unreadable in PC DVD drives). Also, the Xbox is said to use a different DVD file system (instead of UDF).