If you hate the idea of social networking and have never been on Facebook, then Facebook knows nothing about you. Correct? So how come when you set up a profile on the social network for the first time, it can suggest friends for you?

That was what someone who contacted me over the weekend wanted to know.

He described himself as a 30 year veteran of the IT industry who had always been deeply sceptical about social networking. But as an experiment he had set up Facebook profiles, first for himself and then, with permission, for a friend who had also never been near the network.

In each case he was presented with a list of possible friends the moment the profile was created and before there had been any response to the validation e-mail Facebook sends to confirm your e-mail address.

This he described as "really scary stuff for the whole community that do not wish to participate in Facebook social networking, since if they have not registered others can create accounts using their e-mail addresses, and get their list of friends."

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So I decided to try this out for myself. I set about creating a Facebook profile for a friend who is a university lecturer. My friend - let's call her Belinda - had never used Facebook but gave me her permission to put her on the network.

I entered her university e-mail address, chose a password, put in a date of birth, and then was quickly taken to a page suggesting a couple of dozen possible friends.

I rang Belinda and read out the names to her. Three were colleagues, others were present or former students, and some she didn't recognise but assumed they too had been associated with her university. Now at this stage she had received, but not opened, the e-mail from Facebook asking her to authenticate her e-mail address.

So two things are immediately clear - Facebook knows at least something about you the minute you hand over your e-mail address, and it's possible for someone who knows that address to extract some of that information.

My friend was puzzled about how the network knew who she knew. So I got in touch with Facebook to ask some questions. Here they are, followed by the replies:

Q) How does Facebook know about my friend's friends when she herself has never had a profile before I created one?



A) "Suggestions is a feature that helps you connect with people and pages you are likely to know. Facebook calculates suggestions based on the networks you are a part of, mutual friends, work and education information, contacts imported using the Friend Finder, and many other factors."



Q) Shouldn't it be impossible to create a profile - and see someone's "friends" - before you've clicked on the confirmation e-mail?



A) "Accounts that have not confirmed an e-mail address have limited functionality. These accounts cannot communicate with anyone except confirmed friends and the e-mail address does not appear on the profile until it is confirmed."



Q) Doesn't this mean that people's privacy is in some sense under threat even if they are not on Facebook? And doesn't this lay people open to the threat of identity theft?



A) "This is no different to how someone could create a fake e-mail account in someone else's name. Facebook has always been based on a real name culture. This leads to greater accountability and a safer and more trusted environment for our users. It's a violation of our policies to use a fake name or operate under a false identity, and we encourage people to report anyone they think is doing this, either through the report links we provide on the site or through the contact forms in our Help Centre."

As far as I can see Facebook is saying that my friend's friends had probably uploaded the contents of their address books onto the site, including her e-mail details. So when I used that e-mail to sign her up, the network matched it up against anyone who had that address in their contacts and suggested a connection.

Sinister? The man who contacted me at the weekend certainly thinks so, but my friend the university lecturer told me that she had mixed feelings: "Intellectually, I can see I should be concerned about this threat to my privacy, but in practice I am not too worked up about it."

But what's clear is that even if you think Facebook knows nothing about you, it probably does - because your friends have chosen to tell the network about you.

