Visits to torrent sites have doubled over the last year, with TV drama Heroes the most popular illegal download, according to research firm Big Champagne.
Around 55 million people downloaded Heroes, with 51 million watching the second-rated program, Lost.
“Millions of television viewers now access free, unauthorised versions of favourite shows at least some of the time,” said Eric Garland, chief executive of Big Champagne. “This is a socially acceptable form of casual piracy – and it is replacing viewing hours.”
Almost half the activity – 47 percent – came from the US, and all but one of the top 10 dramas were American.
The most popular illegal film download was Watchmen, which attracted 17 million downloads, followed by The Curious Case of Benjamin Button with 13 million.
The research found that there was significantly less piracy for live events and sports shows than for film or television dramas.