Wow, a case between an ISP cartel member and a copyright cartel member. Hard to pick one to root for. Somehow neither side managed to make the other side look like the good guy. You'd think ISPs would do their darnedest to make it so they don't have a way of knowing what content is flowing over their pipes, to help avoid accusations of contributory infringement. ALSO: The photo of an Internet Pirate is amazing.
ISPs don't generally go looking for copyright infringement. In order to keep safe harbor protections ISPs are required by law to register with the US copyright office (which requires them to pay a small annual fee) and provide them with a contact address where they agree to accept DMCA notices. The media industry hires third parties who hunt for IPs sharing files and they report them to the ISPs at their registered address which means they now can't pretend they didn't know about it. Of course those third parties aren't very careful about who they accuse of infringement and innocent people and even innocent network printers (https://archive.nytimes.com/bits.blogs.nytimes.com/2008/06/0...) have been accused as a result, but accusations and unproven allegations are all that matter according to the courts (so far)