Social networking market leader MySpace has been hit with four lawsuits in the US separately alleging that site users were guilty of sexual assault. The families behind the suits are seeking damages of millions of dollars.

Each of the four instances involves sexual assaults which took place between young girls and men that the families say they met on the California-based social networking giant. The company is owned by Rupert Murdoch's News Corporation.

The cases join a year-old Texas suit in which a girl's family is suing MySpace over an alleged sexual assault by a man she is said to have met on the site.

The cases involve teenaged girls from New York, Texas, Pennsylvania and two sisters from South Carolina. None is above the age of consent in her state.

The suits allege negligence, recklessness, fraud and negligent misrepresentation by MySpace. "In our view, MySpace waited entirely too long to attempt to institute meaningful security measures that effectively increase the safety of their underage users," said Jason Itkin, a lawyer representing some of the families. "Hopefully these lawsuits can spur MySpace into action and prevent this from happening to another child somewhere."

MySpace last week introduced monitoring software to help parents monitor their children's activities on the site. It said it would release software called Zephyr which will enable parents to see the name, age and location which children claim as their own. It had previously appointed a security chief to oversee site security.

That security officer, Hemanshu Nigam, said that the company takes security very seriously. "MySpace serves as an industry leader on internet safety and we take proactive measures to protect our members," he said. "We provide users with a range of tools to enable a safer online experience."

Nigam said that families must share responsibility for the actions of children on the site. He said that users should apply "offline safety lessons in their online experiences and engage in open family dialogue."

MySpace's Zephyr software will not be available until this summer, the company said. It restricts activities according to the age of a user, not allowing under 14s to have an account and anyone under 16 can only display their profiles to listed friends for example, but it relies on people to be honest about their age in the first place. Zephyr will at least allow parents to see what age their children are claiming to be, said MySpace.

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