MySpace.com is facing pressure after a new round of lawsuits filed on Thursday that allege it failed to protect minors, and experts say the cases will enter murky legal territory.

Four families whose underage daughters were sexually assaulted last year after meeting men in person they had met online on MySpace filed separate lawsuits in Los Angeles Superior Court. Lawyers for the families contend MySpace waited too long to employ security measures to protect underage users.

MySpace, a social networking site owned by News Corp., has upgraded its security features after criticism the site could be used by predators to target children. The lawsuits come in the same week MySpace revealed it would release software, called Zephyr, for parents to monitor changes in their children's accounts.

Some of the issues facing MySpace have been felt by operators of chat rooms and message boards, whose boom with the growth of the Internet saw some companies take evasive measures to prevent problems.

Yahoo pulled some user-created chat rooms in June 2005 after it found content that violated its terms of use. In 2003, Microsoft shut down message boards in 28 countries, citing a growth in pornographic spam and the forums' use by online predators.

Social networking sites, like message boards, aren't bound by law in how they should operate or what security features they must have, said Struan Robertson, senior associate attorney at Pinsent Masons, a U.K.-based law firm that deals with technology issues.

While illegal activity is banned in terms of use agreements, how that activity is prevented is up to the sites. While a Web site can establish access controls and safety features such as age verification, "there are only so many measures that a site like MySpace can take to protect children," he said.

"Moderation is not mandatory, and with MySpace it would be impossible," Robertson said.

The law suits against MySpace pose new legal challenges given a lack of previous cases, said Evan D. Brown, an IT attorney in Chicago with Hinshaw and Culbertson.

"There really is no clear precedent for this now," Brown said. "It's going to be an exercise in analyzing facts and legal principles in the brick-and-mortar world."

At least one U.S. case against AOL suggests MySpace could be in the clear for content posted within its networks.

In 2001, Florida's Supreme Court rejected a negligence suit where a mother alleged AOL failed to close the account of a subscriber who used a chat room to sell obscene photos of her son, who was a minor.

The court found AOL could not be held liable for not policing chat room communications, in line with the U.S. Communications Decency Act of 1996. The act says that a user or provider of an "interactive computer service" cannot be treated as a publisher or speaker of information provided by someone else.

Brown said plaintiffs could opt to make a "premises liability" argument, alleging that MySpace failed to take reasonable care to prevent foreseeable criminal acts. The complex argument could consider a range of factors, such as the incidents of contact on MySpace that end in violence and what security measures MySpace uses, he said.

However, arguing that MySpace has a responsibility to stop people from meeting in the physical world seems "implausible," Brown said.

"I would say that would be an unreasonable duty," he said.