By now, many of you have heard of Prenda Law. The porn-trolling "law firm" spent years sending demand letters to (and filing boilerplate lawsuits against) those who illegally downloaded porn. Many of the letters contained shades of blackmail, with hints that their investigation of the matter would reveal that person's pornographic proclivities to neighbors and relatives if a settlement wasn't reached quickly.
The legal basis of the scheme was simple: The lawyers acquired the copyrights to pornographic films and assigned the rights to a number of newly-formed shell companies, such as Ingenuity 13. Prenda Law would then monitor BitTorrent for IP addresses and file subpoenas to obtain the identities behind the IPs.
The lawyers would then send the blackmail letters, offering to settle for about $4,000. They'd also file boilerplate lawsuits in bulk, hoping for default judgments. If anyone lawyered up and fought the case, they'd drop it and move on to the next porn pirate.