According to analysis from web security company ScanSafe, a third of employers are now blocking social networking sites to prevent staff poking each other in the workplace. Amongst its corporate customer base it has seen the number blocking such sites rise by 17 percent from this time last year.

Poking has become something of a global obsession ever since Facebook threw its doors open to the general public rather than being strictly a plaything of academia. In fact, ScanSafe says that Facebook usage grew by 270 percent during the last year, with 52 million users worldwide. Although MySpace still heads up the social networking space with 114 million users, LinkedIn is fast gaining traction and popularity among the business community.

According to ScanSafe, which provides web malware scanning and web filtering services, the most commonly requested social networking sites among its business-user customers are YouTube, Facebook and LinkedIn, followed by Bebo, MySpace and Photobucket. However, 32 percent of all ScanSafe customers now block access to social networking sites, with MySpace, YouTube and FaceBook the sites companies are most likely to restrict employee access to. LinkedIn comes fourth in the 'most blocked' list.

ScanSafe also found that 54 per cent of customers block video downloads at work, a popular activity on sites like YouTube and LimeWire.

According to Eldar Tuvey, CEO of ScanSafe: "Companies are increasingly concerned about keeping usage in check - not just for security reasons, but for productivity and bandwidth considerations as well. Where there are large numbers of users, there is sure to be malware and other risks, as popular sites attract not just legitimate users but attackers as well.

"Last year, we found that up to one in 600 profile pages on social networking sites host some form of malware, and we have seen several recent instances of malware targeting users of sites including MySpace and Facebook."

Social networking sites are rich pickings for potential attackers, because they provide easy access to millions of people who trust the site they are on and tend to be less concerned or aware of the potential security risks. Tuvey calls for increased awareness around staff using social networking sites - but balancing the risks with the possible benefits: "When it comes to social networking, as long as businesses have the right security processes in place and a clearly communicated acceptable usage policy for staff, employers should remain open-minded to sites that can be used for positive reasons, such as exchanging ideas, recruitment and networking."