The received wisdom that social networking websites are a security threat might be on the wane with the news that one large US software company is actively encouraging its employees to use Facebook.

Turning its back on concerns about security, Serena Software, purveyor of application lifecycle management applications, has even designated Fridays as the time of the week when it wants its 800 employees around the globe to use the website to communicate with one another.

Dubbing this day ‘Facebook Friday’, it has said it wants to encourage employees to use the site at other times of the week as well, and to do so freely and without active monitoring.

Only two months ago, by stark contrast, a poll by security company Sophos suggested that half of companies were now so paranoid about company information, and details of employees, leaking into the public domain, that they were now actively blocking access to such sites.

In tests by the company, Facebook users were easily duped into handing over personal details to a fictitious user named ‘Freddi Stauer,’ an anagram of ‘ID fraudster.’

Although social networking has become a huge phenomenon in companies – IBM is rumoured to have 15,000 active users – few endorse it publically for fear of opening their enterprises to targeted attacks and the risk of attracting the attention of compliance officials.

"Clearly the security is always a concern," says company spokesman René Bonvanie, who describes himself as Serena’s ‘mashup and Web 2.0’ specialist. "But if people want to break security they are going to do it anyway. If they want to steal, they are going to steal," he said.

"The reality is that if I browse Hoovers, I can find out who the employees are anyway," he said of concerns that criminals could identify company personal for targeted attack from Facebook profiles. He said the company had previously used an intranet but that it had not proved popular. However, so far, 60 percent of Serena’s employees had started using Facebook, he said.

"Social networking tools like Facebook can bring us back together, help us get to know each other as people, help us understand our business and our products, and help us better serve our customers-on demand. A corporate culture that fosters a sense of community and fun will ultimately help us get more done. Companies that do not embrace social networking are making a huge mistake," said his colleague and Serena CEO, Jeremy Burton.

Blocking Facebook is, at least, fairly straightforward and can be done without complex technology. Any firewall with URL filtering will be up to the task. But it looks as if the original purpose of the Internet application revolution might at last be turning back the tide of caution that tends to put security worries ahead of almost any other consideration.