Cease and desist

A cease and desist letter is a document sent to an individual or business to stop attempted illegal activity ("cease") and not to restart it ("desist"). The letter may warn to the individual or business that if they do not stop certain behaviour by deadlines set in the letter, then that individual or business may be sued. The same letter may also warn the individual or business to take specified actions in order to avoid being sued. When a cease and desist letter is issued by a public authority, it is called a "cease and desist order".
Although cease and desist letters are not exclusively used for stopping copyright infringement, such letters are also used to protect other issues related to intellectual property. The holder of an intellectual property right (i.e. either a copyrighted work, a trademark, or a patent) may send the cease and desist letter to tell a third party (i.e. an individual or business who is not related to the holder of the intellectual property right) that they are infringing intellectual property. The letter may contain either an offer to license the intellectual property or a very clear threat of a lawsuit. A cease and desist letter often causes both parties to make licensing negotiations, and is very often the first step towards a lawsuit.
If someone receives many cease and desist letters, it will cost a large amount of money to manage them. Each claim in the letters must be evaluated, and the person or group who receives it will have to decide what to do to sort out the cease and desist letter. Either, they would have to obtain an attorney's opinion letter, prepare for a lawsuit, and perhaps start making suitable alternatives that do not break the holder's intellectual property.
Cease and desist letters are sometimes used to intimidate the offending groups and can be used by corporations to relax the online critical speech of such groups. A company owning a trademark may send such letter to them that they are doing trademark infringement, although the actual use of the trademark by the offending group may fall under a fair use exception (which follows, in the U.S., the protection of free speech under the First Amendment).