The search giants Microsoft and Google have taken steps to make it harder to find images of child abuse online.

The move was welcomed by David Cameron, who previously called for action from the companies. The Prime Minister had threatened new legislation if they did not act.

Google and Microsoft, which together account for 95 per cent of search traffic, have made sure that as many as 100,000 search terms will return no results that find illegal material. They will also trigger warnings that child abuse imagery is illegal and offer advice on where to get help.

Child protection experts say that most illegal abuse images cannot be found via web searches anyway, but are hidden on peer-to-peer networks. A June report by the UK’s Child Exploitation and Online Protection Centre (Ceop) showed that images are distributed using encrypted networks. Google and Microsoft have agreed to work with the UK’s National Crime Agency and Internet Watch Foundation to try to take on these kinds of networks.

Microsoft’s PhotoDNA already gives photos unique prints which can be tracked across the web. Google has done similar with VideoID. With this technology it will make trading illegal material even more difficult.