One in four people on the internet have illegally downloaded a film and the problem is set to get worse, said the US movie industry's trade body.
Releases like Shrek 2 have been pirated on the internet
A study released by the Motion Picture Association of America (MPAA) found that film piracy was worse in South Korea, where broadband is commonplace.
The film studios say piracy on the net has cost them billions of dollars.
Last year Hollywood's major studios made a record $10.85bn (£5.8bn) at the international box office.
For the study, the MPAA questioned 3,600 internet users who regularly went to the cinema from across the world. It found that a quarter admitted to having downloaded a film from the internet.
The figure for Korea was much higher, with six out of 10 net users downloading movies.
More worrying for the film industry, many downloaders said they had cut back on trips to the cinema and were buying fewer DVDs.
The extent of film piracy online looks set to increase as more and more people switch to broadband.
The MPAA found that net users would download more films if they could get the movies faster.
"The time barrier should be mitigated as broadband penetration increases and compression technology improves to reduce the amount of time it will take to download the average movie," said the MPAA study.
In a bid to combat piracy, the MPAA has launched a global campaign to hammer home the message that piracy is a crime.
But it could face an uphill struggle in changing attitudes. The survey found that a fifth of downloaders had no qualms about getting hold of a movie before it was released in the cinema.
And a majority said it was OK to download a film once it was available on DVD or video.
The Hollywood studios say piracy is costing them billions, even though box office takings rose by 5% last year.
The MPAA has put the increase down to rising ticket prices, while the number of total tickets sold dropped by 5% internationally and by 12% in Europe.