If you suspect that BitTorrent is an internet-related tool only used for nefarious purposes, you’re not far wide of the mark. But behind its success as a means of sharing copyrighted material amongst thousands of people who should probably know better, there’s a brilliantly-devised piece of software at work which is beginning to be used for legal purposes.

The programs used for torrenting (such as uTorrent for your PC, Bits On Wheels for the Mac, and Azureus for both) aren’t illegal in themselves, any more than a meat cleaver is illegal until you start brandishing one on the high street. So, feel free to go and download one – they come free of charge, after all. But how do they work? Over to reader Tom Brogan: “If someone wants to share – or ’seed’ – a video file of football highlights, they use a torrent program to create a torrent file relating to that video, which is small – usually around 20k in size. When a copy of that torrent file is opened by somone else, they are connected via a tracker to the original seeder of that video, and, more importantly, to everyone else who has opened it, too.” By using a clever system of breaking this file up into small chunks, the torrent then shares the load of distributing the goalmouth action between all its users; as soon as you’ve downloaded a chunk from the original seeder, other people are free then download that chunk from you. It’s a cheap and remarkably efficient method of distribution.

The amount of data being shifted via torrents is astonishing; it already accounts for anywhere between 18% and 35% of all broadband traffic in North America. As a result, legal activity is becoming frenetic. Copyright holders have tried chasing those who run the aforementioned trackers, but as they store none of the copyrighted data the buck tends to be passed to the torrent users, who are generally whistling, hands in pockets and saying “what’s the problem?” Last year the US broadcasting network HBO sent cease and desist letters to various internet service providers to get their customers to stop torrenting, but many just switched their ISP and carried on. And, as reader Sanjit Ghose pointed out, ISPs can’t ban all BitTorrent traffic because there are legitimate uses: properly licensed movies and music are available at bittorrent.com, and many software companies now choose to release software updates using a torrenting system. But now that we’ve downloaded our torrent software, the chances of us using it legally and responsibly are, frankly, somewhere between slim and non-existent.