Facebook, an online community now restricted mostly to high school and college students, will soon throw its doors wide open and welcome millions of Internet users currently left standing at the gates.

The move will allow existing users to invite their now-ineligible friends, but it also risks changing the tone of a community where trust and privacy are key.

Just last week, users revolted when Facebook introduced a feature that allows easier tracking of changes their friends make to personal profile pages.

The change in eligibility will come soon, although Facebook officials were still deciding exactly when.

• Click here to read about how potential employers may be combing through Facebook.com pages to determine hiring decisions.

To join Facebook, a user now must prove membership in an existing network using an e-mail address from a college, a high school or selected companies and organizations. That has largely limited membership to students, along with some faculty and alumni.

As a result, Facebook has fewer than 10 million registered users, compared with some 109 million at News Corp.'s (NWS) MySpace, which has an open-door policy.

With the change, a user can simply join a regional network — such as one for his country, state, metropolitan area or city. No authentication will be performed.

But unlike the case with MySpace and other open community sites, users will be restricted in how much they can learn about others — the way Harvard students can't automatically view a Stanford user's full profile page, which may include photos, contact information and other personal details.

Users will have to agree to grant access, and they may give some users the ability to view only portions of their profiles.

Started by three Harvard sophomores in February 2004 as an online directory for college campuses, Facebook expanded to high schools last September and to selected companies and organizations earlier this year.

Those users have been eligible to join regional networks as well when they graduate or move, and it is those networks that will be expanding soon.

Chris Hughes, co-founder of the Palo Alto, Calif.-based company, said everyone around the world will be covered by one of some 500 regional networks, although some regions may cover one or more countries. U.S. regions, he said, are likely to be geographically smaller.

Facebook's chief executive, Mark Zuckerberg, said users will be restricted in how often they can switch to discourage impostures and pranksters.

Earlier this month, Facebook introduced what they termed a time-saving feature. Users who log on might instantly find out that someone they know has joined a new social group, posted more photos or begun dating their best friend.

All of the information presented had been available before, but a person had to visit a friend's profile page and make note of any changes — for example, noticing that the friend now has 103 friends instead of 102, and identifying which one got added.

Users equated the feature to stalking and threatened protests and boycotts until Facebook, three days later, apologized and agreed to let users turn off the feature so that others can't easily see what they do.

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