The social networking website MySpace has reported a four-fold increase in the number of convicted sex offenders using its service.
The company found more than 29,000 convicted sex offenders in the United States had profiles on MySpace - up from a figure of 7,000 given in May.
MySpace said it was pleased it had identified and removed the profiles of the offenders.
Critics of MySpace call for new laws to make such sites safer for children.
MySpace is a personal website tool allowing people to post blogs, music, and videos.
More than 80 million people have registered a MySpace page. News Corp bought the site for $580m last year.
'Screams for action'
The new figures were first released by officials in two states - North Carolina and Connecticut - which have been pressing MySpace to reveal data about sex offenders found to be using the site.
"The exploding epidemic of sex offender profiles on MySpace - 29,000 and counting - screams for action," said Connecticut Attorney General Richard Blumenthal.
In North Carolina, Attorney General Roy Cooper wants a state law that would require children to obtain parental permission before creating profiles on sites such as MySpace, and require the site to check parents' identity.
He said such a law would mean "fewer children at risk, because there will be fewer children on those web sites".
Under current rules, users must be over the age of 14 to register with MySpace.
In a statement, MySpace said: "We're pleased that we've successfully identified and removed registered sex offenders from our site and hope that other social networking sites follow our lead."
There are about 600,000 registered sex offenders in the United States.