Twitter: Email addresses and phone numbers may have been used for advertisements

The email addresses and phone numbers of Twitter users, which are intended for the use of, for example, two-factor authentication, may have been used to serve users with targeted advertisements on the platform.

Twitter suggests that it has recently discovered that its email addresses and telephone numbers have been used ‘inadvertently’ for its Custom Audiences and Partner Audiences. This allows advertisers to serve targeted advertisements to users based on the marketing lists, on which, for example, the e-mail addresses and telephone numbers are collected. Advertisers can also target their advertisements to groups suggested by third parties.

According to Twitter, things went wrong when an advertiser uploaded his marketing list. Twitter says it may have linked people on its platform to that list at the time, based on the email address or phone number that users use for security purposes. The messaging platform says this was a mistake and apologizes.

Twitter cannot say how many people were directly affected by this flaw, but according to the company, personal data was never shared with external partners or any third-party partners. Twitter says steps have been taken to prevent such an incident from occurring again. Since September 17, email addresses and phone numbers collected for security purposes are no longer used for advertising, Twitter said.

Facebook was criticized a year ago after it was found to similarly use security phone numbers to target ads. This also happened if the users had not provided the data to Facebook themselves. That happens when a user shares their contacts with the phone number of another person with a Facebook account; Facebook then links that number to that account, even if the owner of that account has not shared anything.

In principle, targeted advertising with telephone numbers takes place via their own list of telephone numbers that companies have. They don’t get to see the phone numbers of Facebook or Twitter users, but they can supply their own list and if there are matches, those people are presented with an advertisement.