The attackers attempted to use automated technologies to link AT&T telephone numbers with online accounts, spokesman Mark Siegel said in a statement sent to SCMagazineUS.com.
Less than one percent of AT&T wireless subscribers were affected by the breach, according to the company. AT&T reported having more than 100 million wireless subscribers at the end of the third quarter, meaning one million subscribers may have been impacted.
The Dallas-based telecommunications giant said it is still investigating the incident to determine the source and intent of the attempted hack.
Affected account holders are being notified “out of an abundance of caution.”