Phaedrus, with its history first accepted, says an article in Ars Technica, from which he extracted a piece relevant to almost anyone with an Internet connection:

A lawyer file sharing has admitted this week that addresses IP are not by themselves identify a person accused of sharing online copyrighted material.

To find out who actually shared the pornographic film in the center of the case, counsel for Gibbs Brett Steele Hansmeier LLC told the judge (PDF), it is necessary to search all the computers in the household of the subscriber.