A vendor hack has resulted in the data of millions of AT&T customers being stolen.

AT&T is sending emails to around nine million customers to alert them of the theft of their data.

The attackers did not breach AT&T directly but compromised the systems of a marketing vendor used by the US telecom giant.

All impacted users had CPNI (Customer Proprietary Network Information) stolen, including phone numbers, full names, and email addresses. A smaller...