Facebook allows people to search out others by their email addresses – and won't let them opt out

Feature could have substantial privacy implications for anyone using the site

(Getty)

Facebook is letting people be found with just their phone number – and there is no way to turn it off, according to users.

The site collects people's phone numbers as part of a security setting, called two-factor authentication, which texts people when they try to login to make sure only someone with access to their phone can login to their account. Some users are forced to turn that on in order to use their Facebook, while everyone is encouraged to use it to keep their accounts secure.

But Facebook is using those same phone numbers to allow people to look up others, it has emerged. And it offers no way of turning it off, even if people are aware of it and want it to stop.

In practise, the tool means that anyone who has given their number to Facebook can be found using it, which could have substantial privacy implications for anyone using the site.

The issue was raised after Emojipedia founder Jeremy Burge tweeted about the discovery. Though the feature is not new, it is not immediately obvious to anyone using the site.

"For years Facebook claimed the adding a phone number for 2FA was only for security," he wrote. "Now it can be searched and there's no way to disable that."

Facebook does offer the option to hide the phone number from the public and limit it only to friends. But there is no way of turning it off entirely.

He noted that a phone number could also serve as a way for different companies to link people's activity across a variety of different platforms, allowing people to be tracked around the internet.

"Using a phone number to sign up for services has been the single greatest coup for the social media and advertising industries. One unique ID that is used to link your identity across every platform on the internet," he wrote.

"That is why every startup wants your phone number."

Facebook does allow people to use other forms of two-factor authentication, allowing them to avoid adding a phone number. The company supports authentication apps, for instance, which stops Facebook from getting hold of any other personal details.