It had to happen sooner or later. Half of employers have banned the super-addictive Facebook social networking site at work, according to a new survey.

Security firm Sophos, which conducted a global poll of 600 employees, reports 43 of people were unable to access the site - let's call it "Crackbook" - due to blocks, with another seven percent saying they did have some, but only limited, access.

Facebook is compelling enough to be both of enormous potential business value and a big drain on productivity in companies that allow open web access.

In the UK, we're all getting addicted to the site as new and old friends have piled on this year in a few months of extraordinary growth - doing the job Friends Reunited always wanted to but never fully managed.

Funniest of all - eight percent of the half of employees who do have full access to Facebook say the site gets the green light at work because their bosses fear a revolt from staff.

It's true - you can't part a Crackbook addict and her social network. They turn in to an angry mob; I've seen it happen.