ACAS chief executive John Taylor said: "Online conduct should not differ from offline conduct. Employees should assume that everything they say on the internet could be made public, and should think whether they want their colleagues or boss to read it. They might not mean it, but what they post could end up being seen by billions of people worldwide."

According to Palo Alto Networks' May 2011 Application Usage and Risk Report, Facebook and Twitter are in use at 96 percent of organisations.

Panda Software's Social Media Risk Index says one third of small to midsize businesses have succumbed to malware infections distributed via social networks, while nearly one out of four organisations lost sensitive data when employees spilled the beans online.

Sam Kinstrey, managing director at 2e2 Training, said there was "a clear need for social media policies and training" in many workplaces.

Social media use by an employee to help them in their professional lives can "bring huge benefits to an organisation", he said, adding: "We need to remember that working practices have changed. An employee might look at Facebook during the day but at the same time, they might be looking at their work emails in the evening."