The copy protection technologies from SunnComm, Macrovision and Sony DADC differ in subtle ways. There are, however, some similarities. Many come with two sets of recorded music -- songs in the unprotected format that plays whenever the disc is inserted into a CD or DVD player, and a separate "session'' of compressed, copy-protected files that open when the disc is inserted into a computer.
When will they ever learn? They won't, they will just keep trying and trying and trying to enforce control over your computer.