Strike 3 has filed over 11,000 lawsuits. They now believe they have evidence linking your IP address to illegally downloaded adult videos, made by them, through an internet file-sharing site known as a BitTorrent site, where content is shared for free.
They will seek to show that a chain of evidence connects your IP address to a torrent site that you have visited for the purpose of downloading their content without paying for it and that they can trace each title they allege you have downloaded to your IP address.
Their evidence is gathered through the use of proprietary software designed specifically to gather infringing IP addresses from the torrent sites and then connecting that address to the illegal downloading of their movies.
The subpoena you have been informed about is their first step in the process of bringing evidence against you to court.