ALBANY — New York officials started sending letters yesterday to more than 25,000 registered sex offenders, telling them to disclose all their Internet user names as part of an effort to keep them from trolling social networking Web sites to meet children.

“The playground of today is not just on the street corner,” Attorney General Cuomo said. “The playground of today is cyberspace.”

Those screen names will be made available to networking sites. Mr. Cuomo, who pushed the measure, said two popular sites, MySpace and Facebook, have agreed to use the information to remove those users.

A new law signed yesterday by Governor Paterson also generally prohibits various offenders on parole, probation, or conditional discharge from using the Internet to contact anyone under 18 or visiting pornographic Web sites. That includes some of the 6,660 higher risk, or Level 3 offenders, others whose offenses were against children and those who used the Internet to facilitate their crimes.

Sex offenders were already required to provide the state Department of Criminal Justice Services with their Internet accounts and screen names, a spokesman, John Caher, said. DCJS lists their names, addresses, and photographs in the public portion of the registry, which totaled 26,773 on Monday. Letters began going out yesterday reinforcing the requirement and informing offenders they must now also provide all additional screen names or e-mail addresses they have for chat rooms, instant messaging, or social networking, he said.

Under the new law, registered sex offenders must also disclose all their user names and e-mail accounts for the purposes of chat, instant messaging, or social networking. If they create any new online profiles, they must notify the state within 10 days or face prosecution for a new felony.

Mr. Paterson recounted an earlier legislative discussion where he’d been surprised to learn sex predators had a nearly 90%recidivism rate. Every parent shares the same fear when their children go online, he said. “The very, very serious fear is that they are vulnerable to the disguise and misuse of the Internet by convicted sexual offenders for harm.”

Mr. Paterson said he would also consider new legislation pushed by a group of Republican state senators to curb video violence on the Web. The measure would establish an additional felony for committing assault in New York while recording it for distribution and a new felony for persuading others to do so.