Copying music has been commonplace since the invention of the tape recorder, whether the music industry liked it or not.
Many people have built up digital music collections
Then, in the 1990s, we suddenly found that our computers could copy CDs.
A black market in cheap copies immediately arose, leading to police raids around the world.
Even so, album sales in the world's main markets continued to climb until they peaked in 1999.
But since then a new way of copying music, and anything else you can load onto a computer, has taken hold.
Peer-to-peer (P2P) websites are based on the single simple concept of individuals sharing what they have on their computers, rather than keeping it to themselves.
The software is easy to find and download from the internet. Most set up a special folder or offer the user options for which files they want to share.
Instead of searching the web, P2P users then search each others' computers.
You can download any of the files you find for free, as long as the people who already have them are online.
Networks using the latest technology allow each file to be downloaded from lots of computers at the same time, which speeds up copying.
A typical pop song can be acquired in this way in less than a minute.
They can then be transferred to an MP3 player - like the iPod - or burned to a CD.
It has been estimated as many as nine out of 10 files shared in this way are music.
While P2P services themselves may be legal, sharing copyrighted songs is not.
Last month a survey in America suggested one in four people under the age of 24 shared music for free.
That figure drops to less than one in 20 for everyone older, and it is a similar picture in Europe.
Tom Dunmore, editor of Rip 'n' Burn, the first magazine in the UK dedicated solely to the new download culture, says the industry ignored the phenomenon at first.
"They were thinking it was going to be a very small number of people who would be tech-savvy enough to use services like peer-to-peer, which at first weren't particularly easy to use.
"But they didn't realise how quickly the thing would snowball, and how appealing the idea of free music would be to a whole generation who had PCs in their bedrooms or at school, and who were finally getting broadband into their homes."
At first the music industry targeted P2P networks themselves, and in 2001 met with some success when the original Napster file-sharing service shut down.
But technologies moved on and other networks emerged to fill the void.
Since then, many judges have been reluctant to hold the sharing networks accountable for what their users download. Kazaa has just won such a ruling in Australia.
One of the most popular P2P networks, eDonkey, says it is doing nothing wrong.
"Our technology is just that. It's a piece of software that allows users to store information and share files with each other regardless of the type of file they're sharing", says Sam Yagan, eDonkey's president.
"Just like a Xerox machine or a VCR allows people to manipulate their media, so does our file-sharing software."
Legal action against individuals soon followed. In the US this meant a wide range of people being threatened with court action, a policy which was seen by many as a PR blunder.
Tom Dunmore says: "I think that people who are downloading music also buy music. You do risk alienating your entire audience by suing some downloaders, because you are suing music lovers."
Now the record companies are targeting uploaders - those people who make available thousands of tracks for copying.
The UK industry thinks the bulk of the tracks traded for free are provided by just 15% of users.
But free file-sharing does not just have legal pitfalls.
File-sharing is vulnerable to viruses and spoof files
Advertising campaigns are trying to warn P2P users of the risks of downloading viruses, which may be hidden inside the files they are trying to copy.
It is a fair warning. File-sharers often do not know what they have got until they open it, and by then it is often too late.
Free P2P networks are frequently bundled with spyware and advertising.
This is a concoction the record labels are keen to exploit to persuade us to pay for our music.
"When you download from a legal service you get what you pay for", says Matt Phillips, of the British Phonographic Industry (BPI).
"You're not going to get a spoof file or a virus, or something else unmentionable which I'm sure most parents wouldn't be too chuffed about their children downloading."
While he is aware that some of the BPI's members may be putting spoof files into P2P networks, Mr Phillips says this is something the BPI cannot take a view on.
And the record labels do not shout about their relationship with a small company called Overpeer.
Based in New York, Overpeer enables some big industry names to use spoiling tactics and make the free-song swappers lives a misery.
Scott Mills: Download-only files can be attractive to the record buyer
By creating fake or "spoof" files it tries to swamp the swappers networks with useless content - anything from white noise to a repeated music sample.
Marc Morgenstern, CEO of Overpeer, says: "What we do is make the P2P experience much more frustrating and much less rewarding.
"Someone clicks on our file, expecting it to be a pirate file, but instead they encounter a decoy file.
"This is a file which may contain an audio sample or a game demonstration but does not contain the content that's expected."
Perhaps the best weapon against music file-sharers are the new legal download sites.
This year has seen an explosion of them from 20 to 100 across Europe and America, offering high quality downloads for less than a pound or a dollar.
As Ed Averdieck, of digital music distributor OD2, points out: "You can buy three or four downloads, different tracks, for the same as you used to pay for a CD single."
And the idea of downloading has been embraced by the industry in some countries so much that they even have their own download chart like the one broadcast to the UK by BBC Radio One.
Radio One DJ Scott Mills says the download chart has featured many older records that have dropped out of the singles chart.
And, particularly in the run up to Christmas, more artists are releasing tracks available for download only or for download before you can buy in the shops.
This, he says, is quite attractive to the record buyer.
There are still some songs you can hear on the radio but not legally download online because a few copyright agreements with some artists have yet to be agreed.
But while illegal file sharing remains very popular, this is the first year that the music industry has truly embraced downloading and offered a legitimate alternative.
Across the UK, alongside the traditional record token, you can now buy download vouchers to use online.
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