Half of the site's users are 35 or older, according to comScore Media Metrix's analysis of its U.S. Internet traffic measurements. Only 30 percent are under 25 despite a common belief that the site is mostly populated with kids and young adults.

Just a year ago, teens under 18 made up about 25 percent of MySpace, the popular online hangout run by News Corp. That's now down to 12 percent in the comScore analysis released Thursday.

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By contrast, the 35-54 group at MySpace grew to 41 percent in August, from 32 percent a year earlier.

"This analysis confirms that the appeal of social-networking sites is far broader," said Jack Flanagan, executive vice president for comScore, adding that the data suggest that social networking is becoming mainstream.

Sites such as MySpace encourage their users to stay in touch by offering tools such as message boards, photo sharing and personal profile pages. Members can expand their networks by adding other users as friends and, in turn, connecting with their friends.

The study was based on comScore's regular panels for measuring Internet audiences, rather than MySpace's registration information, where users often lie about their age.

ComScore also reported that MySpace had 56 million unique U.S. visitors in August, much less than the 100 million-plus registered users MySpace has worldwide. The company has said about 10 percent of its users are abroad. A better explanation for the gap is the fact that many people have multiple profiles, each counted separately by MySpace but not by comScore.

Facebook, meanwhile, had 15 million unique visitors, Xanga 8 million and Friendster 1 million, according to comScore.

Of the four social-networking services studied, Xanga skews youngest, with 20 percent of its users under 18 (though MySpace and Facebook both had more under-18 users overall given its larger size). Facebook, which started as a hangout for college campuses, had the biggest share among those 18 to 24. Friendster and MySpace had high appeal among the 25 and up.

Flanagan said the analysis shows each site occupying a slightly different niche, allowing all to coexist rather than compete.

"MySpace.com has the broadest appeal across age ranges, Facebook.com has created a niche among the college crowd, Friendster.com attracts a higher percentage of adults, and Xanga.com is most popular among younger teens," he said in a statement.

The numbers, however, do not reflect Facebook's recent relaxation of eligibility requirements. Before, users generally had to be part of a college or high school network, although some companies and organizations were later added. Starting last month, a user only needs a valid e-mail address.