This is pure speculation from them. In fact if you once shared those files, the info (depending on ISP and country) may stay 10 years in ISP servers (law may require in some countries like UK). So you may get this letter in 9 years as they have proofs against you. But they must prove that this recording really happened and that you used it. This means they must have the record of your entire transmission. You can have deleted it or the person who got it (if someone did) after downloading which they have to prove you or the other didn't. This could even have happened without your knowledge (you didn't know how it worked, or did you show them you did with a webcam). Your ISP server may also have malfunctionned or you simply got your IP spoofed by hackers, and they have to prove they haven't.

See how impossible you can make the life of their lawyers. They do know it, so you haven't got to admit anything.

Now something more. You are on the right side by sharing your files. Your government is on the bad side, by selling your freedom of fair use. Under DMCA law which is not constitutional (this is like saying white is white), father copying a DVD (by using a couple of batch lines written in text mode for Perl) on hard disk so his son could watch the movie fluently on his PC could be denounced by some of his child friends and sent for 5 years to prison like some murderer. If he made some new Perl code or modifies some he got and his child shares it with friends, he may be sentenced to life prison with the new 'anti-hacker laws'.

Do you subscribe to the point of view of your government or do you want to share the fight for freedom by fully using p2p. 10 years ago a technological revolution brought freedom against controlled data transmission. Big companies (bribing governement) want to get that freedom off and use that technology to sell your acquired freedom by using inapropriate laws and principle against it. They say copyright is property, but copyright is a privilege they acquired against copy and nothing more. They want to be able to educate you to like and *** on any Boring Spears so they only have to pull a trigger every 3 month to get their cash. But as you think Boring S. is junk and shabby, you just want to hear radios with whatever pleases you and considering Boring S. is crap you just want to hear how crap it is as she publicly spreads her noise everywhere without people will, but don't want to spend one penny on it. On the contrary THEY want to empty your pockets to show your friends that as the ads and radio spamming were telling you all day that BS is mandatory. This is why they are after internet radios now either. They just don't want you to be able to choose anymore !

About copyright and license. One may know that those privileges were granted for the only sake of economical efficiency to promote the invention of any kind. This enables someone to openly create without the fear of being copied (not stolen). This has nothing to do with property, but this word is used today as "intellectual property". This is something very wrong as you may not own ones mind if he has the same thoughts as you do. This is just where this laws are getting us : SLAVERY. Not physical slavery, but more sophisticated, psychological slavery.