An unfamiliar face catches your eye as you scroll down your timeline – someone you may know, according to Facebook.

Yet, on closer inspection you have no mutual acquaintances and there are no obvious links as to why this person has been suggested as a ‘friend’.

Exactly why did Facebook recommend this person to you? What information did it use to do so? And how can you limit the information available to it, should you so wish?

“Facebook wants people to spend the longest they can on the platform, so that their advertisers pay more,” says Jodie Cook, managing director of JC Social Media in Birmingham.

“Facebook uses any information it can glean from them, including locations, events, external apps plus anything else its algorithms pick up. There really is no hiding."

This week we will publish a series of articles throwing a spotlight on the social media giant’s use of data.

We began with a look at how it targets you via tagging and location and now move on to the accessing of phone contacts and email accounts.

Facebook failed to respond to two separate requests for comment.

Phone contacts

Give Facebook access to your phone contacts and it will use them to help widen your network.

“Facebook won’t import the numbers but will use them to see if the phone numbers are associated with a profile on Facebook and then these people will come up in ‘people you may know’,” Carmen Lascu (pictured below), a social media expert and blogger based in Southampton, told BusinessCloud.

READ MORE: How Man City are using social media to understand fans

Carmen Lascu

Facebook confirms some of this, stating: “We collect contact information you provide if you upload, sync or import information (such as an address book) from a device.”

Email accounts

Email addresses are also covered by Facebook's above statement, it seems.

“When we’ve had somebody new at work, if they’ve got an associated email address and then I’ve used Facebook on the mobile app, that’s brought that person up as a suggestion,” Nik Hewitt, digital strategist at Tank PR in Nottingham, revealed.

One way to avoid this happening the other way round would be to avoid giving your mobile number to Facebook and not allowing access to your phone contacts and email addresses, he suggested.

Acquiring this information from your contacts isn’t a continuous process though, according to Pamela Hopkinson, director of Social Media Solutions in Barnsley.

She says it happens at regular intervals – which could raise problems. 

“If an ex was stalking you and you’ve deleted their number there’s every reason to assume that the number was collected from your phone when that person wasn’t causing a problem,” she said.

“That means that person could still be suggested as a person you may know.”

Tomorrow: Focus on internet searches