Computer and software companies eventually sought to limit the use of
their software to authorized computers and paying customers. Releasing only
the binary files compiled from the source code, rather than the source code
itself, helped them to achieve this goal, as well as protecting their code and their
ideas from their competitors. Another issue involved copyrighted material.
Operating systems and other programs can limit the ability to play back movies
and music or display electronic books to authorized computers. Such copy
protection or digital rights management (DRM) would not be effective if the
source code that implemented these limits were published. Laws in many
countries, including the U.S. Digital Millennium Copyright Act (DMCA), make
it illegal to reverse-engineer DRM code or otherwise try to circumvent copy
protection.