Nearly one in five (19 percent) of global firms are blocking access to social media sites such as Facebook and Twitter during work hours, says Clearswift.

Research by the security software firm revealed that the number of companies stopping staff accessing these sites has risen from nine percent in 2010.

Furthermore, more than two thirds (68 percent) of firms worldwide now monitor employee activitiy on the web and over half (56 percent) block access to some web sites.

Despite this, 54 percent still believe web collaboration is a 'pivotal' tool for business and 31 percent of UK-based firms expect to invest more in social media during the coming year than they did last year.

Clearswift said a 'socianomic paradox' had emerged, as on one hand 80 percent of managers realise social media tools generate benefits for firms but 48 percent have proactively identified social media use in the workplace as a concern.

Just 48 percent of firms believe the benefits of social media outweigh the drawbacks. However, only one in seven companies are using it as a tool for growth.

Security concerns are the biggest issue about social media that's worrying managers, with 57 percent rating this as their biggest fear, while 48 percent are worried about the loss of confidential data and 43 percent are concerned about hacking. Half of managers also believe employees are oblivious to security concerns.

These fears are well places as more than one in five (21 percent) employees admit to not being concerned about security when using the web and email while 31 percent admit they believe security is an employer responsibility.

Furthermore, there is a clear divide between managers and employees about the use of social media in the workplace, as nearly half (48 percent) of managers surveyed say that social media is either allowed or encouraged within their organisation, but only a quarter of employees agree.

This divide also affects the use of personal devices at work, as six in ten firms state they allow or encourage use, but only 40 percent of workers think this is the case.

Nearly a quarter (23 percent) of staff also revealed they believe social media and the use of personal devices are leading to a longer working day, while seven in ten claim email and social networking affects concentration in the workplace.

Nearly nine in ten (87 percent) companies also admitted they are so concerned about security and data loss its hampering adoption of new technologies.

"It's clear that we have seen some significant changes in attitude to social media in the last twelve months," said Andrew Wyatt, chief operating officer, at Clearswift.

"Businesses have reacted to the series of high profile data leaks and have become increasingly nervous about its usage in the workplace. Rather than embracing new channels of communication, companies have clamped down and become overtly defensive which is consequently stifling potential avenues of growth."