More than 3,500 registered New York State sex offenders have been kicked off Facebook and MySpace in the first sweep of the sites’ databases since a state law went into effect last year, the state attorney general’s office announced Tuesday in Williamsville.

That includes 350 sex offenders in the eight counties of Western New York and 43 percent of the roughly 8,100 sex offenders registered statewide.

Standing before reporters, students, parents and child advocates at Williamsville South High School, Attorney General Andrew M. Cuomo said he and his staff believed that the number of predators caught on social networking sites would likely be high.

“We had suspicions that it was bad,” he said at the news conference, “but frankly, it’s worse than we even thought.”

Many sexual predators who are on probation or parole are barred from social networking sites under the state’s tough Electronic Securing and Targeting of Online Predators Act, or e-STOP, which Cuomo authored.

Convicted sex offenders who are on probation or parole are barred from social networking sites in cases where the victim was a minor, the Internet was used to commit the offense or the offender was designated a level 3 — highest level — offender.

Among those caught with online profiles were sex offenders previously charged with crimes against a 14-year-old boy and a 10-year-old girl, Cuomo said. “These are truly dangerous sex offenders,” he said.

Under e-STOP, convicted sex offenders are required to register their e-mail addresses, chat-room names and other identifying information with the Division of Criminal Justice Services. Failing to do so is a felony.

That database of information has been available to the administrators of social networking sites for several months, Cuomo said.

Facebook and MySpace — the country’s two most-well-known social networking sites —have adopted the new protections available under the e- STOP law.

Facebook identified and disabled accounts linked to 2,782 registered sex offenders in the state, and MySpace identified and disabled the accounts of 1,796 sex offenders.

Some registered sex offenders were connected to accounts on both sites, Cuomo said. In total, 3,533 individuals were purged from the sites during the sweep. Those who had accounts with either Facebook or MySpace were then reported to law enforcement for violating the terms of their probation or parole, he said.

Laura Ahearn, executive director of Parents for Megan’s Law, said the threat of cybersex offenders is real and growing.

“What’s terrifying is that the number of aggressive solicitations to actual in-person contact is increasing for boys and has nearly doubled for girls,” she said.

She and many other child advocates have gone on record praising Cuomo and the state’s e-STOP law, the only one of its kind in the country.

“Before e-STOP, sexual predators trolled in social networking Web sites looking for innocent victims,” she said. “With e- STOP in full force, Attorney General Cuomo has sent a clear message that there is a new sheriff in the cyberworld and he is protecting our most vulnerable.”

Ahearn then introduced a sexual assault survivor in New York State, who offered her comments by speakerphone. The woman, identified as “Jane,” developed an online relationship with a man who was a registered sex offender and was eventually charged with multiple counts of sexual assault against Jane.

The woman said the man she conversed with online seemed so sympathetic to all her hopes and fears as a teenager that she eventually agreed to meet him.

“I had no idea that I was about to meet a registered sex offender who had assaulted a 13-year-old girl,” she said. “What occurred after we met will haunt me forever, much longer than any jail sentence he could ever serve.”

She praised Cuomo for the e- STOP law.

“Before, there was nothing stopping sexual predators for doing what he did to me,” she said.

Cuomo said that even though MySpace and Facebook are making use of e-STOP voluntarily, 17 other social networking sites contacted by the attorney general’s office have yet to do so, including some better- known sites like Flickr, Classmates.com and Friendster.

“We beseech these other social networking sites to do the same thing that MySpace and Facebook did,” he said.

His final comments were aimed at warning parents and children of the dangers of the Internet. As a parent of twin girls in their first year of high school, he said he knows how difficult it is to talk about Internet safety with young people.

“You’re talking about a side of humanity you wish you didn’t have to explain,” he said.

Students at the news conference said the e-STOP law makes a lot of sense and should be picked up by other states, the way state laws banning texting while driving have gained momentum.

“It’s a very practical law,” said Clark Zhang, 17, president of the Student Congress at Williamsville South. “It’s something that should be enforced for all of those Web sites.”