While comic book sequel Spider-Man 3 made $60m (£30m) at the American box office this weekend, things could have been a lot, lot better. Millions of people have already illegally downloaded the movie for free over the internet, possibly depriving the film of over 50m box office dollars.

A visit to torrent website Mininova this morning reveals that it is one of many sites acting as a gateway to hundreds of different pirated copies of the third Spidey sequel. In total, two million people have downloaded Spider-Man 3 torrents through Mininova alone. Assuming that all these people downloaded instead of paying at the box office, this piracy has potentially deprived the movie of up to $30m.

And this doesn't even take into account the number of people who have downloaded Spider-Man 3 torrent files from other websites, of which there are many. In fact, in the time it has taken you to read just this far down the page, another 300 people will have completed their illicit Spider-Man 3 downloads.

Then you have to add on the number of people who have downloaded the movie through other P2P services. And all those who've bought dodgy pirated DVD versions.

Widespread robbery

Spider-Man 3 was released worldwide last week. Within hours, many crafty criminals had used camcorders to record low-quality pirated versions of the movie. They then uploaded them to the web for mass download.

And despite the terrible quality of these files, millions of people are still happy to download and watch them - because they're free.

Many argue that movies are now making more money at the box office and from DVD sales than ever before. But under these circumstances, it's not hard to imagine that summer blockbusters like Spider-Man 3 could be making a hell of a lot more money if the piracy problem were to disappear.