For people like me who'd never heard of DMCA before, this is what Wikipedia says:
"The Digital Millennium Copyright Act (DMCA) is a United States copyright law that implements two 1996 treaties of the World Intellectual Property Organization (WIPO). It 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 circumventing an access control, whether or not there is actual infringement of copyright itself. In addition, the DMCA heightens the penalties for copyright infringement on the Internet. Passed on October 12, 1998, by a unanimous vote in the United States Senate and signed into law by President Bill Clinton on October 28, 1998, the DMCA amended Title 17 of the United States Code to extend the reach of copyright, while limiting the liability of the providers of on-line services for copyright infringement by their users."
About as clear as mud to me - maybe some USA people could translate.
PS: This helps a bit: http://www.citmedialaw.org/legal-guide/responding-dmca-takedown-notice-targeting-your-content. Seems like you're guilty till proven innocent. Or maybe I haven't understood???