'Stop poking me, Sally!'

Some 50 percent of workers are blocked from accessing Facebook by business owners worried about the site's impact on productivity and security.

Employers are increasingly putting policies or access controls in place to ban its use in the workplace, according to research from Sophos, reports MarketingCharts.

In a poll of 600 workers, 43 percent said their company was blocking access to Facebook, while an additional 7 percent reported that usage of the social networking website was restricted, and only those with a specific business requirement were allowed to access it, Sophos said.

In contrast, 50 percent of respondents said their company did not block access to Facebook, with 8 percent specifying the reason as fear of employee backlash.

A second Sophos poll showed that 66 percent of workers themselves were concerned that their colleagues were sharing too much information on Facebook, which could lead to identity theft and targeted phishing attacks against the company.

According to Sophos, a large number of Facebook profile pages contain users' current employment details, which could be used together with other stolen information by cybercriminals bent on corporate fraud, or to infiltrate company networks.

Last week, Sophos published research showing that 41 percent of Facebook users were prepared to divulge personal information to a complete stranger (in the form of a small plastic frog called Freddi Staur).

"Companies are split on the question of Facebook. Some believe it to be a procrastinator's paradise, which can lead to identity theft if users are careless. Others either view it as a valuable networking tool for workers or are too nervous of employee backlash if the site is suddenly blocked," said Graham Cluley, senior technology consultant at Sophos.

"Companies need to make their own mind up as to whether they want to allow their users to access websites like Facebook and MySpace during office hours. If workers are allowed to be given access to these sites, then it's imperative that they are taught best practices to ensure that they are not putting their personal and corporate data at risk. Five minutes spent learning the ins-and-outs of Facebook's privacy settings, for instance, could save a lot of heartache later."