The movie industry has turned its legal campaign against net piracy to TV file-sharing sites.
Dr Who appeared on the net even before it was broadcast
Six BitTorrent sites hosting links to others with illegal copies of TV shows have been targeted in lawsuits by the Motion Picture Association of America.
It is a shift in focus for the MPAA. Since it started legal action against file-sharers in December, its targets have been film indexing sites.
A recent survey said TV programme downloads had risen by 150% in a year.
About 70% were using BitTorrent sites, according to the Envisional research. Of the total downloaders, 18% were within the UK, it said.
In March, TV downloading made headlines with the appearance of the long-awaited new series of Doctor Who on the net before it was even broadcast.
The MPAA said it was worrying.
"There are thousands of people in the entertainment industry who are working to develop, produce, and promote television shows. Those shows and those jobs are worth protecting," said Dan Glickman, MPAA chief.
"Every television series depends on other markets-syndication - international sales - to earn back the enormous investment required to produce the comedies and dramas we all enjoy and those markets are substantially hurt when that content is stolen."
'Want to make it worse'
It is the first time that the MPAA has specifically gone after TV-oriented networks in this way, which it says are used by thousands daily.
It has, however, targeted BitTorrent sites before. It has filed 100 lawsuits against operators of BitTorrent server sites since December.
Copies of popular US shows, such as Desperate Housewives and 24, regularly appear hours after they are first aired on networks in the US, and downloaded by fans around the world eager to see the latest episodes.
Because TV programmes are usually shorter than films, they are processed - or digitised - quickly.
Those people with increasingly faster broadband connections can download episodes in very little time. But the MPAA says its action to hit those running servers which link to copyrighted material has slowed this.
The percent of working servers has dropped by more than 40% since it started action, said the MPAA.
"Since we began shutting these sites down, the time that it takes to download a file on BitTorrent has increased exponentially which means the experience of downloading copyrighted films and TV shows is not what it used to be," said Mr Glickman.
"We intend to make it even worse. Protecting the television industry is essential."
With BitTorrent software, server sites do not host the files being shared. Instead, they host links, called "trackers" which tell people where to go to get the files.
More than 90% of the sites that the MPAA has sued so far have been shut down entirely.
The sites which have been closed, such as LokiTorrent, UK Torrent and s0nicfreak, now carry warning messages from the MPAA that read: "You Can Click But You Cannot Hide."
The MPAA says it wants to encourage legitimate download sites instead. Several TV companies are experimenting with legal peer-to-peer based downloads, including the BBC.