Staff who use Twitter and other social networking sites while at work are costing UK businesses £1.38bn every year, a report has said.
Over half of those surveyed admitted using social networking sites during the working day for personal use.
On average those people spent 40 minutes per week on these sites.
IT services group Morse, who commissioned the research, said that such online behaviour clearly had a "productivity strain" on firms.
The survey questioned 1,460 office workers.