MySpace has revealed it has identified and removed the profiles of 90,000 registered US sex offenders from its social network in the past two years.

The social network, which had 125 million visitors in December according to ComScore, also said it had blocked the users and passed their details on to law enforcement agencies, following a campaign by attorney generals in the US.

"These convicted, registered sex offenders creating profiles under their own names unmasks MySpace's monstrously inadequate countermeasures," said Connecticut Attorney General Richard Blumenthal, when he started the campaign in the US.

"MySpace must purge these dangerous offenders now - and rid them for good."

MySpace said it has been using Sentinel software, which has a database of names, photos, dates of birth, email and instant messaging addresses of more than 700,000 registered sex offenders in the US, to help identify and block unsuitable members. It also claimed there had been a 36 percent drop in the number of registered sex offenders using the site, despite users as a whole growing 10 percent year-on-year.

"We can confirm that MySpace has removed these individuals from our site and is providing data about these offenders to any law enforcement agency including the Attorney General's in Connecticut," said Hemanshu Nigam, chief security officer at MySpace.

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"MySpace is proud of its leadership position and hopes that Facebook follows our lead in providing their members with the same protections that MySpace, MyYearbook and Bebo have implemented," added Nigam

However, according to John Cardillo, CEO of Sentinel, MySpace's biggest rival, Facebook hasn't been as successful in keeping sex offenders away from the social network. Cardillo, claims he's found thousands of registered sex offenders on Facebook.

Cardillo told TechCrunch: "We found over 8,000 offenders on their site without much effort. My professional opinion is that the real number is 15 to 20 times that."

In response, Chris Kelly, Facebook's chief privacy officer, said: "We have devoted significant resources to developing innovative and complex systems to proactively monitor the site and its users, including those not on a sex offender registry, for suspicious activity - such as contacting minors or users of predominantly one gender".

"If we find that someone on a sex offender registry is a likely match to a user on Facebook, we notify law enforcement and disable the account. In some cases, law enforcement has asked us to leave the accounts active so that they may investigate the user further."

See also: Sex offenders to be banned from Facebook