FACEBOOK'S privacy settings are "a mess" with more than 170 options buried in 50 categories and wrapped up in a 6000-word policy that's longer than the United States constitution.

It's so complicated that social networking experts believe many of the site's eight million Australian users are vulnerable to online predators and scammers despite believing their information is totally secure.

Mark Pesce, one of Australia's leading authorities on social networking sites, said the latest Facebook settings introduced earlier this year made it deceptively difficult for people to limit the exposure of personal information they post.

In what is one of the biggest criticisms of the site, the default privacy settings are open. That means that users must manually adjust 50 privacy settings with more than 170 options to ensure their profiles are open only to desired people.

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Equally worrying is a little-known default setting buried within a user's account giving Facebook permission to share profile information with third-party applications, such as advertisers.

And as if keeping up with all the options wasn't complicated enough, the settings revert to the more open default each time the site is redesigned.

Privacy on the social networking site has been brought into focus following the alleged murder of Sydney teenager Nona Belomesoff.

The man charged over the 18-year-old's death allegedly met Ms Belomesoff on Facebook and used her profile to glean information about her life.

In a statement this week, Facebook said the company was "deeply saddened by Ms Belomesoff's death".

"Nothing is more important to Facebook than the safety of the people who use our site," it said.

But on its own website, Facebook recommends that users leave personal information such as their detailed description and status updates open for everyone to see to "make it easier for friends to find, identify and learn about you".

Mr Pesce said that was dangerous: "If your privacy isn't really, really strict then friends, friends of friends and God knows who else can wander on and learn a lot of things about you."

Mr Pesce said Facebook, which has an estimated 400 million users worldwide, could easily simplify its privacy settings.

"It's a mess. Whether that's intentional or accidental is an open question," he said.