Twitter has e-mail addresses and phone numbers that users have entered to protect their account, unintentionally used for advertising purposes, the company announces on its blog.
Twitter advertisers could target their advertising to users if they upload the same email address or phone number to the social media company. In this way they can, for example, find existing customers or similar people on the social medium.
The data that advertisers have thereby uploaded to Twitter would have been accidentally linked to Twitter users who had provided that email address or telephone number to secure their account.
How long the practice has existed and how many users have seen advertisements in this way is unclear. Twitter reports that the error was resolved on September 17: from that moment the security data will no longer be used for advertising.
Competitor Facebook came in the news in a similar way in September 2018. The company had to admit telephone numbers intended for account security were also used for advertising purposes, after a group of researchers in the United States discovered that.