Facebook users are being warned to check their privacy settings as the networking site opens up profiles to the public.

A new public search feature means Facebook user profiles - showing a photograph and name - will be accessible from search engines like Google and Yahoo within a few weeks.

Users can opt to make their site invisible by adjusting privacy settings on the Welcome Page.

Facebook engineer Philip Fung wrote in a blog post this week that the change is minimal.

"We're expanding search so that people can see which of their friends are on Facebook more easily.

"The public search listing contains less information than someone could find right after signing up anyway, so we're not exposing any new information, and you have complete control over your public search listing."

But others say the public listings put Facebook on a slippery slope to unlocking the huge amount of personal data available on its sites.

Keith Reed, online manager for web security firm Trend Micro, warns of the potential for identity fraud.

"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 told British media.

"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."

Facebook, widely regarded as a more sophisticated social networking site than Bebo or Myspace, is growing daily in both profits and members.

Last month the California-based site attracted more than 30 million visitors and is expected to record profits of over $30 million in 2007.

The opening up of user listings continues Facebook's march into the mainstream.

The site began as an exclusive communication system within Harvard University, but rapidly ballooned to include other universities, then schools, and employees.

In September last year, Facebook opened up to the masses, with a valid email address becoming the only requirement to create a page. While Myspace reigns supreme in the world of cyber networking, Facebook's current growth is unrivalled.

UK figures show over the last six months, Facebook's global audience has grown at 19 times the rate of MySpace: 523 per cent compared with 28 per cent. Bebo has grown 49 per cent in the same period.

This is despite a widely-discussed conspiracy theory that alleges Facebook is the brainchild of the CIA.

Having funded the site in its early days, bloggers argue, the CIA now uses the network to find recruits and monitor the public.

- © Fairfax NZ News