Several former radicals, who have renounced extremism and are now working to prevent radicalization, have signed up for the summit. They include TJ Leyden, a former neo-Nazi who has set up a foundation to combat bigotry; Maajid Nawaz, a former member of the Islamist party Hizb ut-Tahrir; and Susan Cruz, a former member of one of the most notorious Latino gangs in the US.

Ms Cruz said the idea that the children who join the drugs gangs in the US are different to those children attracted to religious extremist groups, and who end up as suicide bombers, was wrong. "They may dress different[ly], their language may be different but fundamentally deep down inside the child that joins a gang is the same child that joins a militia or an extremist religious group . . . they are all looking for the same things," said Ms Cruz, who works with children to steer them away from violent gangs in the US. Shot and imprisoned when she was a gang member in Los Angeles, she said she hoped the summit would find solutions to help children stay away from extremist groups and provide hope that people can change.

Google is interested in the way technology is used by extremist groups to recruit members and by pro-democracy demonstrators in North Africa and the Middle East.