Company are split over what to do about social-networking sites that are costing UK businesses an estimated £6.5bn a year, according to security experts.

The figure is based on the fact that office staff questioned by security consultants Global Secure Systems (GSS), and Infosecurity Europe 2008 admitted spending at least 30 minutes of work time a day visiting sites like Facebook, Myspace and Bebo - equivalent to 10 hours a month, or three weeks a year.

Two of the 776 people questioned spent three hours a day at the sites, and IT directors reckon social networking can use up to 20 per cent of their bandwidth. One big company banned the use of Facebook after discovering that it took 30 per cent of bandwidth.

But Claire Sellick, Infosecurity Europe event director, said administrators are split over the issue, with most IT and security directors wishing to ban use of the sites at work.

"What is also coming across loud and clear is that [human-resources] departments actually welcome the use of these sites - so there is a lot of internal pushing and shoving going,” said Sellick.

GSS managing director David Hobson said social-networking sites have become integral to the way many young staff communicate and work.

He said: "So for some sectors social-networking sites may have a part to play in terms of competitive advantage or used for research or as a marketing tool. It comes down to a fine balancing act - and mostly a case of introducing a 'reasonable use' policy.”

Hobson warned that there are serious security implications: "Hackers, exploiters and extortionists are worming their way into these sites extracting all sorts of information on the members. Our advice as always to anyone using these sites is to give as little personal information away as possible.”