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MELBOURNE - Facebook is shaping up as every boss' nightmare as the social networking website urges its members to hook up with workmates online.

That means millions of corporate dollars could be lost as workers manage their online social life via Facebook, rather than being productive in front of the screen.

Facebook is advertised as a social utility that connects people with friends and others who "work, study and live around them" - although many seem to be doing less work.

Originally a photo-sharing network, Facebook users can now invite others into their personal sites to chat and share information.

An anonymous Facebook user summed up the growing trend: "Of course everyone checks Facebook at work, duh! I don't have neither internet nor a TV at home because I like doing more useful things with my time when I'm off work," the blogger wrote.

And the Facebook explosion has good reason for bosses to stop the onslaught of online chatting at work.

In just two days this month, 7000 people joined Facebook, as they chat with a network of mates - often daily, sometimes hourly.

Internet filtering specialist, SurfControl, estimates the Facebook craze could cost businesses more than A$5 ($NZ 5.75) billion a year.

According to SurfControl figures, if just one employee spent an hour a day on Facebook, it could cost their business A$6200 a year.

With 800,000 businesses in Australia, these figures translate to A$5 billion a year.

"On July 29 there were 195,000 members of Facebook's Australia network. Just over a week later, this number had grown to over 224,000," SurfControl spokesman Dr Richard Cullen said.

"There are Facebook groups dedicated to slacking off at work - some of them are specific to employees of a single company."

Dr Cullen said employers were now resorting to blocking internet use.

"Some employers are blocking the sites, while others have embraced the new, global networking capability and are setting down times when it's acceptable to Facebook," Dr Cullen said.

"If appropriate filters are in place, employees are able to use sites like Facebook and Myspace in their downtime without putting the network at risk."

Australian Industry Group Victorian director Tim Piper said employers had the choice to restrict internet use.

Mr Piper said the group would not endorse a push to block internet use at work.

"It's up to each employer to deal with it in a manner that's appropriate for their staff," Mr Piper said.

Mr Piper said preventing access to troublesome sites could save hours of unproductive behaviour.

- AAP