LOS ANGELES - Microsoft Corp., Yahoo Inc., AOL and two other U.S. Internet companies late on Monday said they are joining forces to fight the distribution of child pornography on the Web.

The companies, which have cooperated in the past to battle viruses, spam and identity theft said they will work with the National Centre for Missing and Exploited Children (NCMEC) on the new effort.

"We believe it is possible to increase the chance that child predators will be caught and provide a deterrent to those who would be tempted to exploit children on the Internet," said John Ryan, chief counsel at Time Warner Inc.'s AOL.

Other participants in the effort, known as the Technology Coalition at NCMEC include EarthLink Inc. and United Online Inc. Members who are scheduled to testify before Congress on Tuesday morning have pledged $1 million in combined initial funding.

Ryan said the coalition's first order of business is to attack the distribution of illicit images of children on the Web by creating a database of signatures or codes that identify known pornographic images so that Internet service providers can spot them and stop them from being shared.

The group will also research and develop tools for law enforcement in addition to studying the technology that predators use to exploit children and to conceal their activity.

NCMEC's CyberTipline collects reports of child sexual exploitation. NCMEC has assisted law enforcement with more than 119,800 missing child cases, resulting in the recovery of more than 102,200 children.