Target Chairman and CEO Gregg Steinhafel says he is "still shaken" by the data breach during the holiday shopping season that compromised the personal information of millions of customers.
"It's hard for me to describe the feeling that came over me," he told CNBC in an interview aired on Monday.
Steinhafel said he has had several "sleepless nights"
and expects more because "we are not going to sleep until we get it right and we regain the trust of our guest."
Target said on Friday that an investigation found hackers stole the personal information of at least 70 million customers, including names, mailing addresses, telephone numbers and email addresses.
That is in addition to its earlier disclosure that as many as 40 million credit and debit cards were compromised between Nov. 27 and Dec. 15 by malware installed on the company's sales registers.
"As time goes on, we're going to get to the bottom of this," Steinhafel said. "We're not going to rest until we understand what happened and how that happened."
"Clearly, we're accountable and we're responsible but we're going to come out at the end of this a better company and we're going to make significant changes," he added.
He did not detail what changes are in the works, saying, "We are in the middle of a criminal investigation as you can appreciate and we can only share so much."
The company, the Secret Service, the Justice Department, and a forensic unit connected to Verizon Communications are involved in the investigation
, reports The Wall Street Journal.
Several states are also investigating the incidents and Target's response, according to the newspaper, with New York Attorney General Eric Schneiderman calling the newest revelation about the theft of personal customer information "deeply troubling."
Meanwhile, the company has not disclosed the estimated costs related to the breach. On Friday, Target cut its profit forecast for its U.S. stores in the fourth quarter by about 20 percent, due partly to a drop in sales after the reports of the cyber-attack.
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