In a short opinion Justice Thomas said ``The provider of a service is contributorily liable for the user's infringement only if it intended that the provided service be used for infringement.'' He compared it to two previous cases, Grokster which found that Grokster was liable because they promoted it as a piracy service, and Betamax which found Sony not liable because even though it is possible to use a video recorder to make pirate copies, it has a lot of other uses like time-shifting for later private viewing. Cable ISPs have a lot of uses other than piracy so it's like Betamax, and Cox wins.

Five justices signed onto that opinion. Justices Sotomayor and Jackson disagreed, saying that while they thought the majority's opinion was overbroad and there could be theories of liability that apply, Cox did not have the intention to aid copyright violators, so they still win. It has a long discussion of other cases showing what would or would not establish secondary liability, involving knowledge and intent, and what seems to me an overblown concern that the majority opinion is so broad that ISPs can now completely ignore DMCA notices.

This seems to me the right outcome. If you have a copyright, it is not anyone's job but yours to police it, and if as is often the case here you can't pin a violation to an individual but only to an IP address, too bad, you don't get to block everyone else on that IP, particularly as here where some of those IPs serve thousands of people at downstream ISPs.