Since these are an attempt at civil prosecutions, if they were to go to court they would be decided on the balance of probabilities rather than beyond reasonable doubt, that is to say if the judge reckons that there's a 51% chance or more that you did it, then you'll be found guilty. However, if you were to receive one of these letters that have been cleared by the High Court, it probably won't contain an awful lot of evidence against you - the times and dates of the alleged file sharing, the title(s) of the works that were allegedly shared, and the IP address who was allegedly sharing the works. Your ISP would have linked your account to the IP address based on the time it was used hence why you can be traced. This proves fuck all; imagine if you live in a shared house and all use the same internet connection, you regularly let visitors connect to your network, or you leave it unsecured - all the smutmongers have done is sent the threatening letter to the bill payer and not the person who has allegedly downloaded the work(s) in question. There is no way for them to actually know or find out who really did it (if anyone actually did anything, knowing that IP addresses can be spoofed). There are only three ways in which this scam works:
1. You want to avoid hassle and pay up without a fuss. Don't do this.
2. You ignore them. ACS:Law won a few cases by default as the defendant ignored all the letters and didn't show up in court. Don't do this either.
3. Perhaps the most important, you give away information that tips that balance of probabilities. This is what the Ben Dover letter is going to try to get people to do:
"In our first letter we seek to find out more information regarding evidence of an infringement of our copyright," said Julian Becker.
"Depending on the response to our letters we will then decide our next action."
The simple answer to this is to deny the alleged offence, refuse point blank to pay them any money under any circumstances, and not to tell them anything. Anything that you do tell them, say about your network set up, who uses your network, and so on will be used against you. You are under no obligation to tell them anything or answer their questions. Their main evidence is an IP address that your ISP said that the account in your name was using. It cannot be connected to an individual user of your network. In summary, tell them to fuck off.*
* OK, caveats apply - look on the internet for a decent template letter response or get a solicitor if you're not comfortable with that. Don't consider this blog as legal advice.