AT&T "does not tolerate unauthorized access to its customers' information or company websites," said AT&T chief privacy officer Dorothy Attwood, in a weekend e-mail to iPad users affected by the breach.
"We will cooperate with law enforcement in any investigation of unauthorized system access and to prosecute violators to the fullest extent of the law," Attwood said.
The FBI last week confirmed it's probing the breach, which was admittedly carried about by self-styled "researchers" at a group called Goatse Security, which maintains a Web site registered in France.
Goatse members have said they were merely attempting to point out security vulnerabilities that could threaten iPad owners.
Attwood, however, called Goatse's actions malicious. "The hackers deliberately went to great efforts" to obtain iPad owners' e-mail addresses, she said.
AT&T said it discovered the breach a week ago and immediately notified affected customers. It also said the vulnerability that allowed the hackers into its computer network has since been fixed.
"This issue was escalated to the highest levels of the company and was corrected by Tuesday, and we have essentially turned off the feature that provided the e-mail addresses," an AT&T spokesman told the Reuters news agency last week.
The list of iPad users whose data may have been compromised includes high-profile celebrities, politicians, and athletes. New York City Mayor Michael Bloomberg, White House Chief of Staff Rahm Emanuel, and producer Harvey Weinstein were reportedly among the victims.
The incident could place further strain on AT&T's partnership with Apple. Many iPhone and iPad users have complained that the carrier's cellular network isn't sufficiently robust to support Apple's millions of customers in the U.S. Complaints range from dropped calls to poor signal quality.
Some analysts have speculated that Apple will soon end its exclusivity deal with AT&T and open up its devices to additional carriers, including Verizon.