Twitter admits it used two-factor phone numbers and emails for serving targeted ads

Twitterhas said it used phone numbers and email addresses, provided by users to set up two-factor authentication on their accounts, to serve targeted ads.

In a disclosure Tuesday, the social media giant said it did not know how many users were impacted.

The issue stemmed from the company’s tailored audiences program, which allows companies to target advertisements against their own marketing lists, such as phone numbers and email addresses. But Twitter found that when advertisers uploaded their marketing lists, it matched Twitter users to the phone numbers and email addresses users submitted to set up two-factor authentication on their account.

The issue was addressed as of September 17, the disclosure said.

Two-factor authentication is an important security feature that makes it far more difficult for hac