By Jonathan Fildes
Technology reporter, BBC News
Software is used to track down the suspected pirates
Around 15,000 suspected pirates may soon get legal letters accusing them of illegally sharing movies and games.
ACS:Law plans to send notes to the accused in the new year offering a chance to settle out of court for "several hundreds of pounds".
A lawyer who has defended people who have received similar letters described it as a "scattergun approach" that would catch "innocent people".
ACS:Law said it was "unaware" of anyone who had been wrongly sent a letter.
Andrew Crossley of the firm told BBC News it was acting to "eradicate" sharing of its client's products.
"We give them opportunity to enter into compromise right at the start to avoid having to deal with it [in court]," said Mr Crossley.
If it went to court and the lawyers were successful, he said, damages "would run into several thousands of pounds".
But consumer group Which? said that it had heard from around 150 consumers who had been "wrongly accused" in similar cases.
"A lot are accused of downloading pornography," Jaclyn Clarabut of Which? told BBC News. "People find it distressing or embarrassing and pay up."
Others, she said, "don't want the threat of court action" hanging over them or cannot afford to pay for a lawyer and settle the claim for the lower figure.
She said that based on previous experience, "a lot of people will be surprised" by the latest wave of letters.
Michael Coyle, lawyer at Southampton based firm Lawdit, described the scheme as "having very little to do with protecting the rights of the copyright holder".
Instead, he said, it was "more to do with making money from alleging copyright infringements on a massive scale".
He has represented several hundred clients who have received letters from ACS: Law and other firms. None of his clients has ever been forced by a court to pay a fine, he said, although some clients had decided to settle out of court.
"This scattergun approach to the file sharing litigation will inevitably result in a large number of innocent parties being issued with a claim for copyright infringement."
ACS: Law are "currently under investigation" by the Solicitors Regulation Authority (SRA), but a spokesperson said it could not divulge any more details about the nature of the complaints. The Law Society has also received complaints.
Mr Crossley said his firm had been targeted by an "internet campaign" and was cooperating with the inquiries.
"It doesn't of itself indicate that I have done anything wrong," he said. "I have no qualms or concerns about what I am doing."
ACS: Law recently obtained two High Court orders that require ISPs to hand over the names and addresses of the account holders for 30,000 IP addresses, a number which can identify a computer on the internet. It is currently preparing three more.
The orders were obtained on behalf of two clients: DigiProtect and MediaCat.
Which? say innocent people have been caught out in similar cases
Both firms are licensees of copyright work. They act on behalf of copyright holders, including various pornography studios, to pursue alleged copyright infringements.
They use software to monitor file sharing networks to harvest IP addresses which are then turned over to law firms to get account details.
"We state that they [the alleged file-sharers] have made available to others via peer-to-peer file-sharing networks various products that they have rights in," said Mr Crossley.
He said these included "games, films and music".
"We estimate that commencing in the New Year we will be despatching circa 15,000 letters in relation to these two orders," he said.
The letters would be used to tell the alleged "file-sharer" that they were thought to have infringed copyright.
It would also inform recipients that a claim may be made against them in court and would "invite" them "to enter into a compromise to avoid any litigation."
The amount would vary, he said, but was typically £300-500.
The money is split between the copyright holder, licensee, the firm monitoring IP addresses and ACS: Law, which operates on a no win, no fee basis.
Concerns have been raised about the technology used to identify IP addresses.
Which? has highlighted various examples of innocent people accused by firms such as DigiProtect .
"Many have never heard of peer-to-peer file sharing," said Ms Clarabut.
File-sharing is not illegal. It only becomes illegal when users are sharing content, such as music, that is protected by copyrights
The crackdown will be aimed at people who regularly use technologies, such as BitTorrent, and websites, such as The Pirate Bay, to find and download files
There are plenty of legitimate services which use file-sharing technology such as some on-demand TV services
"Some are accused of downloading video games but never played a game in their life."
A study published in 2008 by Which? highlighted the case of Scottish couple Gill and Ken Murdoch, aged 54 and 66, who were accused of sharing a video game.
At the time, Mrs Murdoch told Which?: "We do not have, and have never had, any computer game or sharing software."
The letters were sent by another law firm, which no longer represents DigiProtect. Mr Crossley said the Murdochs had been identified because the ISP gave the lawyers the wrong information about the account.
Mr Crossley admitted the account holder may not be the person sharing files illegally. As a result, he said, the letter, would also invite the recipient to name the person they thought was responsible.
The growing popularity of wi-fi means many people share an internet connection. Recent studies have also shown that many people do not password protect their wi-fi connections, meaning they can be hijacked and used for nefarious means.
In addition, technology exists that can hide or "spoof" an IP address.
Mr Crossley said that "spoofing" did not apply for file sharing purposes.
Mr Coyle said he also had reservations about the methods used to identify people and said they had never been challenged in court by experts.
"The last thing they want is this software being examined in a court of Law - it would shoot the goose that lays the Golden Egg," he said.
No court case has ever been fully decided from a letter sent by ACS: Law, he said.
Although Mr Crossley admitted the software had never been analysed in court, he denied it had never been scrutinised.
"Every application submitted to court is supported by an expert report," he said.
The report was compiled by "an independent expert" and confirmed that the "data being collected is accurate".
"That is the starting point for us," said Mr Crossley. "It is very important for us to be accurate. If it is not, everything that comes from that data must be flawed."
Similar concerns are currently being outlined to the UK government which recently outlined how it plans to tackle illegal file-sharers.
The Digital Economy bill recently had its first reading and includes a plan to disconnect persistent offenders.