The safe harbor provisions of the Digital Millennium Copyright Act (DMCA) give online service providers like Twitter, Facebook, and YouTube immunity from liability for copyright infringement by users. As long as a provider meets the requirements laid out in Section 512 of the DMCA, it cannot be held liable for a user’s activity. Those requirements include, among other things, expeditious removal of material once a valid takedown notice is received, and a “repeat infringer policy” that terminates the account of those repeatedly accused of infringement.
“Valid” takedown notices are those that come from the actual rightsholder or an authorized agent of that rightsholder, have all the identifying information required by the DMCA, and are sent under a “good faith belief” that the use of copyrighted material was not authorized by the “owner, its agent, or the law.” However, the threat of liability and the large damage awards possible in copyright cases encourages service providers to take things down quickly in response, even when the notices are flawed.
If a notice causes material to be removed, the user will be notified and given the opportunity to counter-notice. Under the DMCA, if someone receives a false takedown notice, they can send a counternotice. If the other party does not respond with a lawsuit within two weeks, the service provider can restore the content, without fear of liability. Counternotices must contain all of a user’s contact information, and the user must consent to jurisdiction in a United States federal court (either where the user is located or, if the user is outside of the U.S., where the service provider is located). If a user is concerned about giving their contact information, a lawyer can generally act on their behalf.
A counternotice should explain why the use is lawful. For example, it can assert that the material does not belong to the party who sent the notice, that the user has permission to use the material (via a license or some other agreement), or that the user has made fair use of the copyrighted material.
One of the other requirements for safe harbor protection under the DMCA is the aforementioned “repeat infringer policy,” that provides for the termination of repeat infringers in “appropriate circumstances.” The law doesn’t specify precisely what this policy must look like, so each service has their own that you should be able to find in their terms of service. For example, YouTube employs a “three strikes”: three copyright notices within 90 days will lead to a creator losing their account, having all their videos removed, and losing the ability to make new channels.
In theory, successfully counternoticing should prevent your account from being tagged as a repeat infringer. In practice, that does not always happen. Contacting someone for help if this happens is a good move.
Note: Many services use automated systems to detect and remove uses of copyrighted material. This is not related to the DMCA, and the methods for getting your content back up after detection vary from service to service.