Google and Microsoft unveiled measures to block online searches for child sex abuse images on Monday as part of a bid by British authorities to crackdown on Internet pedophiles.
The companies said as many as 100,000 search terms will now fail to produce results and trigger warnings that child abuse imagery is illegal while offering advice on where to get help.
The world's two largest search engine operators' move was a rare display of unity ahead of an Internet safety summit on Monday hosted by Prime Minister David Cameron.
Cameron welcomed the progress to block illegal content but said far more still needed to be done.
"If more isn't done to stop illegal child abuse content being found, we will do what is necessary to protect our children," he tweeted ahead of the summit that will announce a new trans-Atlantic task force to tackle online child abuse. The summit comes after Cameron this summer called on Internet firms to do more to stop access to illegal images. Now both companies have introduced new algorithms that will prevent searches for child abuse imagery.
Google executive chairman Eric Schmidt wrote in Britain's Daily Mail newspaper that these changes had cleaned up the results for over 100,000 queries that might be related to the sexual abuse of children.
"As important, we will soon roll out these changes in more than 150 languages, so the impact will be truly global," he wrote, adding the restrictions would be launched in Britain first then expanded to other languages in the next six months.
Both Google and Microsoft, who were due to join other Internet companies at the summit on Monday, have also agreed to use their technological expertise to help in the identification of abuse images.
Schmidt said Google planned to provide engineers to give technical support to the Internet Watch Foundation in Britain and the U.S. National Center for Missing and Exploited Children, and to fund internships for engineers at these organizations.
Conservative parliamentarian Claire Perry, who is Cameron's adviser on childhood, said British and U.S. law enforcement agencies would back up this effort by tracking pedophiles using the "hidden Internet" or so-called "dark web" of encrypted networks to distribute images of child abuse.
(Reporting by Belinda Goldsmith, editing by William Hardy)