As the first Prisoner of Azkaban bootlegs start circulating on the internet, the US movie industry has launched a campaign to crack down on illegal downloads.

The Motion Picture Association of America (MPAA), a lobby group representing the major studios, yesterday announced a "public education campaign" intended to explain "why movie piracy is illegal, and how it impacts jobs and the economy".

The campaign will be carried in various US print publications, and there will also be ads in cinemas. Two particular targets are university students and parents of teenagers.

Jack Valenti, the MPAA president, said the campaign was aimed specifically at convincing people of the "wrongness" of illegal downloads, but warned that the industry would "keep all of our options open, including legal action".

The studios are in this respect following the lead of the music industry, which has gone through the courts in its attempt to stop file-sharing services such as Napster, and see them replaced with legal, paid-for services. Napster recently reopened as an online music store, while Apple launched its iTunes paid-for service in Europe yesterday.

Similar services for film are in their infancy, but the MPAA cited CinemaNow and Movielink as examples of legitimate sites from which to download movies.