For every video on YouTube, the judge required Google to turn over to Viacom the login name of every user who had watched it, and the address of their computer, known as an I.P. or Internet protocol address.
Both companies have argued that I.P. addresses alone cannot be used to unmask the identities of individuals with certainty.
”—Via:(NYT) And yet the MPAA maintains frivolous lawsuits based on IP address hoping for settlements.