Husbands who secretly watch Internet porn will have to confess to their wives when new family filters come in, UK Prime Minister David Cameron says.

From next year people will have to opt in if they want their Internet service provider to allow them access to pornography at home.

Asked by BBC Radio what that would mean for those who may access such content without their partner knowing, Mr Cameron said they were "going to have to have a discussion" about their surfing habits.

President Barack Obama is closely watching Britain's moves to block abusive images from being seen, and to track down those responsible for making them.

Google and Microsoft today bowed to pressure to rewrite their software to block 100,000 search terms used by pedophiles to access illegal material.