A US federal judge has issued a preliminary injunction barring RealNetworks from selling a computer program that makes back-up copies of DVDs that the big film studios argued could have eviscerated their $25bn in annual sales.

District Judge Marilyn Hall Patel ruled that the software company had violated its licence from the DVD association by allowing anyone to make copies of DVDs, including those that were rented, and then move the copied content between devices such as computers and other players.