So holds today’s California Court of Appeal decision in Digital Music News LLC v. Superior Court (Cal. Ct. App. May 14, 2014). The anonymous commenter was represented by Paul Alan Levy of Public Citizen, who has a fair and accurate blog post about this; here’s an excerpt:

[T]he court decided that the discovery was not relevant to the state court infringement action [and thus the unmasking of the commenter was unjustified] ….
The court went on the say, however, that even if the subpoena met the ordinary test of relevance, discovery to identify an anonymous speaker implicates the speaker’s right of privacy under the California constitution. Consequently, the court had to apply a multi-factor test that requires consideration of the extent to which the party has “a compelling need for discovery,” and whether that need is so strong as to “so strong as to outweigh the privacy right when these two competing interests are carefully balanced.”
In this regard, the court took into consideration not just Escape’s minimal need for discovery, but also the problem that, if the anonymous commenter really was an Escape employee, “exposure could endanger not only his or her privacy but also livelihood.” …

Check out also this: “We will not lightly lend the subpoena power of the courts to prove, in essence, that Someone Is Wrong On The Internet.” I assume from the italics and the capitalization that this is a reference to the iconic xkcd comment. (Note, though, that the line makes sense given the claims in this particular case; if this were a defamation case, there might be something more to it than just “someone is wrong.”)