OTH, the a judge may declare them a vexatious litigant.
said by »legal-dictionary.thefreedictiona···litigant :A legal action or proceeding initiated maliciously and without Probable Cause by an individual who is not acting in Good Faith for the purpose of annoying or embarrassing an opponent.
The U.S. legal system permits persons to file civil lawsuits to seek redress for injuries committed by a defendant. However, a legal action that is not likely to lead to any practical result is classified as vexatious litigation. Such litigation is regarded as frivolous and will result in the dismissal of the action by the court. A person who has been subjected to vexatious litigation may sue the plaintiff for Malicious Prosecution, seeking damages for any costs and injuries associated with the original lawsuit.
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I am not advocating for the illegal downloaders but it seems that these letters amount to nothing more than extortion by the force of legal intimidation. I do not think these copyright holders would like it if the tables were turned on the them and internet users set them up as new revenue stream by baiting them by placing false files that do not contain any copyrighted material. An accredited research should conduct a controlled study by placing files that contain the titles of copyrighted material on a P2P network to cull how many false positives resulted in a threatening legal letter being sent. These false files would simple contain a review of the copyrighted work which under the fair use doctrine would permit the use of such a copyrighted works title which would be contained in the false files title.