DMCA

The Digital Millennium Copyright Act, passed in the United States in 1998 by a unanimous Senate vote to implement the 1996 WIPO (World Intellectual Property Organization) treaties.

Greatly reviled by the Internet and computer savvy, for two reasons:


 * 1) 17 USC 1201, which makes it illegal to circumvent access-control technology, even for otherwise legal purposes. Playing DVDs and many formats of internet videos on Linux is illegal; playing the movie is legal in itself, but you have to break access control in order to play it on Linux. Likewise, it's illegal to play an import video game if you need to get around an access control, even though playing the game is legal in itself. The ostensible reason for this is to stop piracy; but even if you had no intention of copying the DVD or game, you can't play it on anything that works around the copy-protection scheme instead of through it. This also makes legally archiving videogames in formats that are no longer used that were made by companies that no longer exist almost impossible.
 * This part of the DMCA requires that the Library of Congress grant exceptions every three years, but limitations on the exceptions, both in the letter of the DMCA and in the way it has been interpreted, make this useless for consumers (see this PDF link from the Electronic Frontiers Foundation). (Note that the exceptions are often misinterpreted. Doing something covered by an exception doesn't violate the DMCA, but it can still be illegal for other reasons; even with an exception, you can't pirate stuff.)
 * As of July 2010, removing the DRM for personal usage is now fair use.
 * 1) The DMCA clause of concern to internet posters is 17 USC 512, or the takedown provisions. These state that online service providers cannot be sued for copyright violation if they promptly take down copyright-violating material and are not liable to the customer for doing so. The customer can send a counter-notification, if they are aware that they can, but the material will be down for at least 10 days, and the legal burden is much lower on presumed copyright owners than on customers.

Because the law gives providers an incentive to always believe the presumed copyright owner and gives the customer little defense against false accusations, it's often abused by corporations and other organizations to force the takedown of material that doesn't violate copyright; the worst cases (on occasion) take down public domain items or copylefted material. It's theoretically an offence to file a false takedown notice, but to date, only one person has ever sued for such "misrepresentation," and the copyright owner has been fighting tooth and nail--see her lawyers' take for more. The Church of Scientology recently filed takedown notices for anti-Scientology videos on YouTube in the name of a nonexistent law company, confident that there would be no consequences. Fake DMCAs are increasingly common on YouTube as people try to censor those with other opinions, as the mechanics of the law means YouTube must act first and ask questions later, and often surrender the target's personal information on request. One infamous example involved a guy DMCAing a person he didn't like, making up fake rumours about grooming children, and then posting his details before closing his account to escape the backlash. Probably #2 is Kent Hovind's Creation Science Ministry, who filed takedown notices against videos it itself released into the public domain.

On the bright side, at least a notice has to be filed by someone before anything gets taken down. It's because not everyone files takedown notices for everything, and because action must be taken to enforce copyrights, that Fanfic and other unauthorized Derivative works can exist on the internet with any permanence. If the ISPs could get sued for Fanfic their users post, there wouldn't be any Fanfic on most of them. (This is why some varieties of Real Person Fic are hard to find. Real Person Fic risks, not copyright infringement, but libel, and the DMCA doesn't override the libel laws.)