Iowa and 42 other states have reached an agreement with the operators of a popular Web site to crack down on the illegal circulation of child pornography and the sexual trafficking of children. Eric Tabor, with the Iowa Attorney General’s Office, says the deal with Craigslist could help investigators find missing persons and identify exploited minors.

Craigslist will now require parties that post "erotic services" ads to give a working phone number and pay a fee with a valid credit card. Tabor said those steps should cut down on illegal activities and provide police with needed information. All the money generated from the erotic services ads will be donated to charity. Craigslist has also agreed to a community self-policing program.

"This allows users of Craigslist to flag a posting that they think includes objectionable or illegal activity," Tabor said. If a posting receives a certain number of flags, it will be automatically eliminated from the site. Craigslist operators also plan to find ways to quickly spot and block inappropriate content.

Tabor says that effort will involve explorations into new technology to better filter for code words and euphemisms for illegal activity. Craigslist is visited by more than 40 million Americans per month. Police across the country have been arresting people for using Web sites like Craigslist to advertise the sexual services of women and children.