Office workers that spend more than 40 minutes a week on social networking sites like Facebook, Twitter and MySpace are costing businesses around $2.3 billion a year in lost productivity, according to a new survey.

According to the survey by Morse, an information technology services provider, 40 minutes on social networking sites a week is the same as a full working week being “wasted” each year per employee.

Of the 1,460 workers that were surveyed, 57 percent said they used Twitter and Facebook during work hours.

“The popularity of social networking sites such as Twitter and Facebook has grown considerably over the past couple of years. However, with it has come the temptation to visit such sites during office hours. When it comes to an office environment, the use of these sites is clearly becoming a productivity black hole,” said Philip Wicks, a Morse consultant.

Of those surveyed, more than three-quarters said their employer had not issued guidelines on using Twitter. Without guidelines and usage policies, Morse said businesses are to not protecting themselves. This results in a reduction in productivity, brand damage and security risks.

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