Facebook's evolution from online clubhouse to internet powerhouse is raising fears that the social network is trading privacy for profit.

The California company's recent move to become omnipresent with software "plug-ins" that let people's online communities follow them to any website is the latest iteration to raise hackles of privacy advocates.

When Facebook users visit websites with "open graph" plug-ins, on-screen windows show which friends from the social network have gone to those pages and what they had to say about them.

While Facebook co-founder Mark Zuckerberg touted the change as part of an inevitable shift to personalised and social online experiences, some see it as creepy.

"The web is at a really important turning point right now," Mr Zuckerberg said while announcing the revamped platform at an f8 developers conference in San Francisco on April 21.

"We are building toward a web where the default is social."

Privacy advocates maintain that Facebook is betraying members drawn to the service as a way to privately share their lives with friends.

"This is a transition from pretty good privacy to Facebook making categories of information available to construct business deals," said attorney Kurt Opsahl of internet rights defence group Electronic Frontier Foundation.

"It seems that they want to go to sites and say 'We have this treasure trove of user information, what do you have?'" he continued.

The online social network that boasts more than 400 million members worldwide started in 2004 as a way for college friends to stay in tune with one another.

As Facebook's popularity soared it came under pressure to make money.

A Beacon advertising system that automatically shared Facebook users' online purchases with the website was abandoned after outrage about intrusion on privacy.

"It seems like this is the new and improved Facebook Beacon," Electronic Privacy Information Centre staff counsel Ginger McCall said of the open graph.

"It was very much built on 'Here is this thing your friend liked, maybe you would like this too'."

Facebook executives were adamant that this isn't a money grab, saying they built no revenue component into the open graph platform.

The website's online advertising model is expected to generate more cash as Facebook becomes a bigger part of people's lives.

The number of websites using Facebook social plug-ins has rocketed to more than 50,000 from just 75 when the feature launched.

Mr Opsahl and Mr McCall pointed out that Facebook has not disclosed financial terms of deals with partners.

"Facebook is entering into business deals where the Facebook part of the transaction is user information and the other party's part is unknown," Opsahl said.

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