Twitter collects data for security reasons, but they inappropriately used some of that information to target advertisements.
Twitter apologized for its ‘error,’ but didn’t say how many users saw targeted ads because of this data collection.
Per a Twitter spokesperson, "When an advertiser uploaded their marketing list, we may have matched people on Twitter to their list based on the email or phone number the Twitter account holder provided for safety and security purposes. This was an error and we apologize.”