More than 2,000 O2 customers will receive letters accusing them of illegally downloading porn films.
The firm behind the films - Ben Dover Productions - had originally applied to the High Court to pursue 9,000 cases on behalf of a range of copyright owners.
The judge threw out all claims apart from those relating to Ben Dover and watered down the wording of letters.
Parent company Golden Eye did not rule out the possibility that it would be pursuing other ISPs in the future.
To date, it has only requested a court order to pursue alleged copyright infringers on O2's network but this may be extended to other ISPs.
"Golden Eye (Int) Ltd continues to monitor all ISPs for our titles and pursue online and physical forms of piracy of our content," managing director Julian Becker told the BBC.
Letters seeking recompense for alleged copyright offences will start going out to 2,845 O2 customers in August.
The Citizens Advice Bureau has agreed to help those who feel they have been wrongly accused.
The judge who granted permission for the case to go ahead has put strict limitations on how letters are worded to avoid the "pay up or else" style letters sent by law firm ACS Law.
Golden Eye will not be able to demand a one-off £700 fine as it had originally wished, instead money owed will be determined on a case-by-case basis.
The letters also make people aware of the help available to them from Citizens Advice, with links to the website and telephone numbers.
And perhaps most crucially the letters cannot hold the bill payer liable if someone else used their internet connection to download illegal material.
The final letter, a copy of which has been obtained by the BBC, reads: "In the event that you were not responsible for the infringing acts outlined above, for example, another member of your household was the user of the computer, you should make full disclosure to us of the other parties at your residence using your internet connection."
It is not clear how the bill holder should respond if they think that material was downloaded by someone illegally accessing an unsecured home wi-fi connection.
Citizens' rights group Consumer Focus, which has followed the case closely, is pleased by the concessions.
"We do not condone copyright infringement, but innocent people should not feel bullied into settling claims and they must be made aware of where to go for help," said Mike O'Connor, chief executive of Consumer Focus.
"That is why we are working with the Citizens Advice service to provide clear advice to consumers about what to do if they are accused of copyright infringement," he added.
The group has also written to the UK's major ISPs asking that they make sure that any application to hand over consumers' personal data is supported by appropriate and consistent evidence of possible wrongdoing.
O2 is believed to be in the process of handing over names and addresses to Golden Eye.
It told the BBC: "We have no option but to comply with this court order and will be co-operating fully."