Twitter says an ‘error’ in its ‘Tailored Audiences and Partner Audiences advertising system’ inadvertently used the information provided by users for security reasons to run targeted ads based on the advertisers’ own marketing lists. The social networking company also said that it does not know how many users were impacted by this error. Twitter assured that no personal data was ever shared externally with its advertising partners or any other third-parties that used the Tailored Audience feature. Last year, Facebook was also caught using phone numbers provided by its users for 2FA protection; FTC accused the company of intentionally using that data for advertising purposes.
Source: https://thehackernews.com/2019/10/twitter-advertising-privacy.html