Content Scrambling System (CSS)
  Audio and video scrambled.

  Uses a set of 40 bit keys to descramble.
    Including :
      1 key for actual player.
      1 key for Movie title. 

  Files can be copied but will not play correctly except from DVD disc.

  The data stream read off of the DVD is not playable until decoded with the 
  keys,
    So cloning the data as it is read is useless.

  DeCSS - this has been broken.   
    It is illegal to distribute the executable decryption program

    However, the source code or algorithm is protected by free speech?

This has been replaced by Cryptomeria cipher on HDDVD.

 and 

BD+ on BlueRay.
  BD+ is virual machine that is part of the dvd player system and reads
  executable code off of the DVD which determines if it was copied.

  Cracked as of December 2008.