system
Given the following post, respond as if you're commenting on Reddit:
human
How does a person get caught pirating music/movies?
gpt
There are probably other tactics, but here's the one you hear about the most (because it's the slimiest and probably also most common):

So you download something illegally from bittorrent.  Anyone else who is downloading from that torrent can see a list of IP addresses (think mailing address, but on the internet) that are also downloading and uploading the torrent.

What the lawyers of copyright holders do is connect to torrents and see who is uploading and how much they're uploading: the more they upload the easier it is to prosecute.  They write down all of the IP addresses, make a big list of them, and sue them all as John Does.  They tell the judge "These people are stealing our content" and the judge writes a court order to the internet service provider saying that the ISP has to identify the subscriber who was using that IP address at the given time.  

Now that the lawyers have a list of people, they update their lawsuits with the real names of the people and send them letters saying they can fight or settle.  A lot of people settle, so the lawyers make a major profit doing this.  It's basically some law firms' entire business model.