Popular internet sites against child pornograpgy

The world's leading internet companies are in secret talks to create a universal system that could eradicate millions of child abuse images from the web.

Facebook, Microsoft, Google, Twitter and at least three other major companies have signed up to - or are in discussions about - a plan aimed at tackling the spread of abuse pictures on their sites, according to industry sources.

It would see the creation of a single database of the "worst of the worst" images that will be maintained by Thorn: Digital Defenders of Children, a Los Angeles-based charity founded by the Hollywood actors Ashton Kutcher and Demi Moore. The project is an unprecedented industry-wide effort to deal with paedophiles using the web to share images of abuse.

Julie Cordua, executive director of Thorn, said: "This has the goal of cleaning this horrific content off platforms ... with the goal of the identification of victims."

Currently, each internet company has its own process to identify and remove explicit pictures from its sites but for legal and technical reasons, they have not shared details of the photos they have found.

The new plan will see each web group share its private lists of abuse images with a central repository held by Thorn. Each company can gain access to the master database for review. It means that if Facebook finds an explicit image on its pages, Google and Microsoft could also prevent copies appearing on their sites.

Thorn was founded by Kutcher and Moore in 2009, after they were moved by a documentary on sexual slavery of children in Cambodia. Though the couple have since divorced, they still work together as board members.

Sources said that the internet companies had been in tense negotiations for about nine months, with some signing legal agreements not to publicly discuss the project. Those with knowledge of the talks said secrecy was required to ensure the rival companies could have frank discussions about the topic.

To join Thorn's project, each company has adopted Microsoft's PhotoDNA software. By using this technology, once a child abuse image is found, a "hash", or digital signature, is created. This allows companies to use hashes to identify and remove copies of offending pictures quickly.

Because it is illegal to hold the actual child abuse images, Thorn's database will be made up of these digital signatures. Facebook, a long-time user of PhotoDNA, is believed to have been among the first companies to begin testing the system.

Google is understood to have signed up to the project in the past few weeks and will begin trialling it this month. The search giant has its own software to spot abusive images, identifying about 100,000 so far. Google has decided to use Microsoft's PhotoDNA to create a mirror of this list to provide to Thorn.

All images will also be sent to the US police for investigation. However, it is understood that executives at Britain's Child Exploitation & Online Protection Centre have also been briefed.

Google confirmed that it was part of the Thorn database project. Though declining to confirm their involvement, Microsoft, Twitter and Yahoo! said that they were participants in the charity's "technology task force" which discusses online protection issues. Facebook said: "We are committed to using technology as a force to protect children."

John Carr, who advises the British Government on online protection issues and is a board member of the UK Council for Child Internet Safety, said that the database was "a fantastic development".

He added: "It is a major step forward in the fight against the rise of child abuse images online."