The number of people using Facebook has nearly doubled in the past year, confirming the site's position as the social network du jour.

In May 26.6 million Americans visited Facebook, an increase of 89 per cent on the same month last year. Among users aged 25 to 34, the increase was 181 per cent, according to research conducted by comScore.

The site is still most popular with people aged 35 and older, who account for 39 per cent of its visitors (10.4 million), but the 25-to-34 category grew from 1.1 million to 3.1 million. The number of users aged 12 to 17 rose from 1.6 million to 4.1 million, an increase of 149 per cent.

The average user now spent 3hr 6min on the site each month, the research suggested.

ComScore attributed Facebook's growth to its decision in September to open registration to the general public. Previously, a valid e-mail address from a university or selected group of schools and businesses was required.

"Given its roots as a college networking site, Facebook has historically shown very strong skews toward the 18- to 24-year-old age segment, Jack Flanagan, executive vice president of ComScore Media Matrix, said. "Since opening registration to everyone, the site has seen visitors from all age groups flood in."

Worldwide, Facebook's subscriber base still trails that of MySpace – with 38.8 million users compared with MySpace's 105 million, according to ComScore – but Facebook's growth rate is nearly 20 times that of MySpace, according to another internet research company, Nielsen/Netratings.

Last week an American academic said that Facebook had become the network of choice for middle-class users, while MySpace was home to "Latino/Hispanic teens, immigrant teens, alternative kids, and others who didn't play into the dominant high school popularity paradigm."

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