The Digital Millennium Copyright Act (DMCA) is a United States copyright law that implements two 1996 treaties of the World Intellectual Property Organization (WIPO). basically, the DCMA makes it illegal to steal and use another person's copyrighted material.

The law criminalizes production and dissemination of technology, devices, or services intended to circumvent measures (commonly known as digital rights management or DRM) that control access to copyrighted works. It also criminalizes the act of avoiding an access control, whether or not there is actual infringement of copyright itself. Overall, the DMCA heightens the penalties for copyright infringement on the Internet.

This site has some good information about the DCMA and how it can help people who create content.