Facebook, the hugely popular social networking site, risks provoking anger from its users by opening up details of individuals to the web at large.

A new Public Search Feature will soon mean that basic Facebook user profiles – carrying names and photographs of the sites members – are accessible through search engines such as Google, Yahoo and MSN.

The move appears to be designed to drive more users to the privately-owned site in an effort to boost advertising revenues, but has already sparked privacy concerns.

Facebook attracted more than 30 million visitors last month, but is expected to make a profit of only $30 million (£15 million) this year on revenues of $150 million.

Analysts suggest Facebook is far from realising its earnings potential. The network is regarded as a potential goldmine to advertisers because it contains a host of data on its users, such as their birthdate, interests, events they plan to attend, holidays and musical tastes, as well as numerous photographs.

However, previous Facebook changes in policy have sparked discontent among its users.

In September, the site's community revolted when Facebook unveiled a News Feed feature, which updates a users’ list of contacts on changes made to his or her profile page. Hundreds protested against the move – somewhat ironically, using Facebook to do so.

Security experts have also voiced misgivings over the amounts of data available on social network sites, which are visited by more than six million Britons a month, and are still growing rapidly, according to Ofcom, the media watchdog.

Keith Reed, the online manager for Trend Micro, the web security group, said: "Social networking sites should be a source of fun, not worry, but there are people out there who spend their time trying to exploit people through their private information."

He added: "Facebook users often provide details such as mobile numbers or employment history and these can be used to hack or steal a user's identity. We would want it to be harder for ID thieves rather than make it easier."

Facebook said: “The Public Search Listing of a profile shows the profile picture thumbnail and links to interact with a user on Facebook.

“People will always have to log in or register to poke, message or add someone as a friend. A user can also restrict what information shows in their public listing by going to the search privacy page. For instance, if a user does not want their profile picture to be shown, they can uncheck that box under “What people can do with my search results”.”

In another departure from past policy, non-Facebook members will also be able to trawl member profiles – a task for which you previously had to be logged in to the site.

The wealth of personal information being entrusted to social networks has attracted attention from advertisers and would-be mischief makers alike.

Virgil Griffith, the American who built the WikiScanner site, which unveiled scores of embarrassing amendments made to entries on Wikipedia – and the people who made them – told Times Online that he is likely to turn his attention next to the "treasure trove of information that people give away" on social networking sites such as Facebook and Bebo.

"I think you could do some very interesting things there – you have huge amounts of information openly available; it's not like you have to do anything naughty," he said.

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