Sydney - Workplaces that try and stop employees using their computers for blogging, online shopping, social networking and other private purposes might be making a mistake, an Australian researcher says.

Around a quarter of Australian firms try and prevent workers from going online during company time by blocking YouTube, Facebook and other entertainment sites and threatening retribution for errant surfers.

"People who surf the internet for fun at work - within a reasonable limit of less than 20 per cent of their total time in the office - are more productive by about 9 per cent than those who don't," said Melbourne University 's Brent Coker.

Rather than sapping productivity, he argues, employees who do a bit of sly surfing during office hours are simply recharging their batteries.

"What we think is happening is that the internet is an enjoyable activity," Coker said. "It increases people's concentration and resets it back to almost 100 per cent - much faster than other forms of breaks taken during the day."

There's a catch: Coker estimates that 14 per cent of people haven't the discipline to take a short break and would troll the net all afternoon if they weren't stopped.

Richard Cullen, a manager at Sydney business consultancy SurfControl, agrees that it's not wise to impose a blanket ban. A better way forward is to negotiate with the workforce what amount of time was acceptable and what wasn't.

But Cullen can't go all the way with Coker.

"Facebook is the new and costly time-waster," Cullen says.

Using Facebook and other social networking sites in company time may be costing local companies an annual 5 billion Australian dollars (3.9 million US dollars) in down time, he warned.