The Digital Millennium Copyright Act or DMCA is a United States copyright law that has been in effect since October 28, 1998. In short, it was an act to update U.S. copyright laws to fit with, at the time, a growing number of pirate websites and copyright infringement websites.
The DMCA tightened penalties for uploading, storing, and distributing copyrighted material online. It also makes circumventing anti-piracy or copyright protections on digital medias such as DVDs, CDs, etc illegal.