UK Prime Minister David Cameron, who had called for action from the firms, has welcomed the move. However, he warned it must be delivered or he would bring forward new legislation. In July, Cameron called on Google and Microsoft's Bing - which together account for 95% of search traffic - to do more to prevent people getting access to illegal images. He said that they needed to ensure that searches which were unambiguously aimed at finding illegal images should return no results.
Now both companies have introduced new algorithms [software instructions] that will prevent searches for child abuse imagery delivering results that could lead to such material.
Microsoft, which in a rare display of unity is working closely with Google on this issue, says its Bing search engine will also produce clean results. The company said it had always had a zero tolerance attitude to child sexual abuse content and had been putting in place stronger processes to prevent access since the summer.
Later on Monday, the two companies will join other internet firms at Downing Street for an Internet Safety Summit.
