JK Rowling has won her claim that a fan violated her copyright with plans to publish an A to Z of Harry Potter. A US judge ruled today that the unauthorized guide would cause her irreparable harm as a writer.

Rowling filed a lawsuit against RDR Books, a Michigan-based company, last year over the Harry Potter Lexicon on the grounds that it lifted huge portions of her stories without adding any original thought or interpretation. She called the project "wholesale theft of 17 years of my hard work".

A district court in the same circuit as this court decided the Seinfeld Aptitude Test case (Castle Rock Entertainment v. Carol Publishing Group, 150 F.3d 132 (2d Cir. 1998)) would have had a hard time finding fair use here. If multiple choice questions based on 'Seinfeld' infringe on the show, then encyclopedia entries based on Harry Potter probably do, too.