Facebook 2FA phone numbers searchable, users can't opt out

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Just because someone has your phone number does not mean they should be able to look you up on Facebook and find your account, so you can imagine all the different problems surrounding this issue. But Facebook will even let you be targeted for ads through phone numbers INCLUDING THOSE PROVIDED *ONLY* FOR SECOND FACTOR AUTHENTICATION, ' Tufecki added in a follow-up tweet.

But by signing up to the feature, a user's phone number becomes linked to their profile.

The good news is that while you can't opt out, you can control who can look up your profile using your phone number. But there's no way to hide it completely.

Quoting the above tweet, security expert and academic Zeynep Tufekci said, "Using security to further weaken privacy is a lousy move-especially since phone numbers can be hijacked to weaken security".

'Facebook 2FA numbers are also shared with Instagram which prompts you "is this your phone number?" once you add to FB, ' Burge added.

It is worth noting that Facebook set the "look up" settings to Everyone by default.

In September, Gizmodo reported that Facebook also uses that security information to target adverts: if a business has a phone number for a potential customer, they can upload that number and target that customer with adverts - even if the number is only in Facebook's systems because of the security policies.

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Facebook had partly disabled such phone-number searches in the past, preventing people from finding someone's profile directly from their number: in April 2018, the ad biz said it had switched off phone number search following the Cambridge Analytica scandal, citing abuse.

Users are only given three options: Everyone, Friends of friends, and Friends. Last year, the company had pestered users into registering their phone numbers for two-factor authentication.

To disable the phone number look-up feature, open the Facebook menu and select "settings".

You may well have opted to maintain an element of privacy by omitting personal information such as your address and phone number from your profile.

In any event, it may still be possible however to abuse Facebook's friend-finding feature by uploading large numbers of contacts via a mobile phone in the hope that Facebook will return a useful response for some of them.

Not mentioned on its help page is the fact that Facebook uses phone numbers for advertising.