ACS Law are the worst kind of legal sharks. They've been chasing people for royalty payments on behalf of a german adult film company, with the threat of legal action.
They have no basis in law to persue these claims, and cannot take anyone to court for non-payment.
I feel sorry for the poor people who's dirty laundry has been exposed to the idiots who frequent 4Chan (don't visit this site if you don't want to see the underbelly of society), but I hope ACS Law get a serious spanking of the data Commissioner for their basic lack of data security...
That is only after they have identified the IP number. They then get a court order for the ISP's to provide names and addresses linked to the IP adress.
My question was how do they match the IP number to an illegal download. I believe the ISP's hold information on sites visited, e-mails sent/received etc, but it seems to me as though ACS are able to get this info as well, then get the court order to obtain the name and address of an account holder.
Using a bit torrent client you can list all IP addresses that are uploading the file to your computer. It's then an easy job to match the IP address to an ISP, then obtain a court order to force the ISP to release the customer's details.
The ease of tapping into an unsecured WiFi connection is the main reason why no-one has been successfully prosecuted for file sharing in this country.
ACS Law are simply using scare tactics to extort money from people, they're nothing less than gangsters...