Sophos has published new research that indicates that corporate IT departments view Facebook as by far the biggest security risk for businesses, which might explain why so many ban usage of the social networking site.

Among 500 firms that were polled, 60% thought that Facebook was the biggest danger, compared to 18% for MySpace, 17% for Twitter, and 4% for LinkedIn. It's not clear where the extra 1% has gone - Friendster, perhaps? The reason for the danger is the plethora of malware, spam and phishing risks on the network. On top of that, Facebook is the biggest social network out there - ten times larger than Twitter with a massive 350 million users.

Sophos' Graham Cluely said: "Facebook is by far the largest social network - and you'll find more bad apples in the biggest orchard. The truth is that the security team at Facebook works hard to counter threats on their site - it's just that policing 350 million users can't be an easy job for anyone. But there is no doubt that simple changes could make Facebook users safer".

In Sophos' report, the company added: "Social networking sites are now a vital part of many marketing and sales strategies. Therefore, they cannot be blocked—but they cannot be allowed to drain company resources or used as vectors for data loss or malware penetration. A unified approach providing sensible, granular access control, secure encryption and data monitoring, and comprehensive malware protection is mandatory for businesses to operate flexibly in the modern socially networked world".