Surveillance in the workplace costs $525m

Bosses keeping tabs on their employees' use of email and the internet are having to fork out $5.25 per head to ensure their big brother status, according to a survey from the US.

The Privacy Foundation reports that up to 100 million workers worldwide are being continuously monitored at work, accounting for a worldwide spend of $525m - $140m of which is being spent on surveillance software.

The Privacy Foundation said the falling costs of surveillance software account for employers showing an increased interest in monitoring their employees.

However, the Privacy Foundation warned employers that by storing audit trails of employee activities, they might be inadvertently maintaining the very evidence that could be used against them for any future litigation.

Some of the companies listed by the Foundation who monitor employees include: American Express, 20th Century Fox, Barclays, Duracell, Glaxo Wellcome, Marriott, Nike and Texaco.