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Target on Friday revised the number of customers whose personal information was stolen in a widespread data breach during the holiday season, now reporting a range of from 70 million to 110 million people.

The stunning figure represents about a third of all American adults at the low end, and is nearly three times as great as the company’s original estimate at the upper end. The theft is one of the largest ever of retail data.

Target’s announcement disclosed a vastly expanded universe of victims and revealed that the hackers had stolen a broader trove of data than originally reported. The company now says other kinds of information were taken, including mailing and email addresses, phone numbers or names, the kind of data routinely collected from customers during interactions such as shopping online or volunteering a phone number when using a call center.

Target on Dec. 19 confirmed reports that payment data was stolen from about 40 million customers who shopped in its stores in the United States from Nov. 27 to mid-December.

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As its investigation into the theft continued, the company said it had found that an additional quantity of data, collected over time on 70 million people and stored separately from the in-store data, was stolen.

The latest subset of potential victims includes customers who may not have shopped at Target during the holidays.

Although there is probably some overlap between the two groups, the company said it did not know the extent.

When Target’s security breach became public in mid-December, customers flooded help lines, the company’s website and Facebook page expressing worry and irritation. It now appears that customers steered clear of Target stores during the last days of the shopping season, as suggested by the company’s statement Friday that sales declined noticeably after the disclosure.

The effect of the data theft has reached far beyond one of the nation’s largest retailers.

Major credit-card companies and banks have been issuing warnings about potential fraud to customers and providing them with new cards and account numbers as a precaution. Some banks have limited cash withdrawals. As banks and companies continue to monitor customers’ accounts for suspicious activity, the Secret Service and the Justice Department have opened an investigation.

“This will impact many Target business partners — Visa, MasterCard and the host of banks and credit agencies that now have to keep an eye on the 110 million customers now vulnerable to identity theft,” said Hemu Nigam, founder of SSP Blue, a security and privacy consultant. “It affects more than Target customers, it affects mortgage lenders and car sales. It affects the entire economic infrastructure.”

Fraud experts said the information stolen from Target’s systems quickly flooded the black market. On Dec. 11, Easy Solutions, a company that tracks fraud, noticed a ten- to twentyfold increase in the number of high-value stolen cards on black-market websites, from nearly every bank and credit union.

The company apologized again Friday for the broadening violation of its customers’ privacy.

“I know that it is frustrating for our guests to learn that this information was taken, and we are truly sorry they are having to endure this,” Gregg Steinhafel, Target chief executive, said in a statement.

Security experts say clever hackers could potentially piece together customers’ stolen information for identity theft or for use in a spearphishing attack, in which hackers send highly tailored emails to victims asking them to click on a link or download an attachment that, once opened, gives hackers a foothold into their computers and employers’ networks.

Target has been working with a forensics team at Verizon, and it has consulted with Mandiant, the security firm specializing in data-breach recovery, which recently agreed to be acquired by FireEye, a security software company, for close to $1.1 billion.

After the initial breach, Target said it had protected customers’ payment information with encryption and that it had stored the keys to descramble it on separate systems not affected in the breach.

But the encryption algorithm Target used to protect that data — a standard known as triple DES, or 3DES — is vulnerable in some cases to so-called brute force attacks, when hackers use computers for high-speed guessing. In a breach on Adobe last year, hackers were able to bypass 3DES encryption through brute force attacks and exposed tens of millions of Adobe passwords within weeks of the breach.

On Friday, a Target spokeswoman would not comment on whether the second batch of information stolen from its 70 million customers was encrypted.

Security experts say the number of Target customers exposed could still grow.

“Like a natural catastrophe, usually a low number of breached records is reported and, as the story unfolds, the number of compromises grows and grows,” said Anup Ghosh, founder of Invincea, a security software company.

Ghosh said he suspected hackers might use the trove of email addresses to send spoofed correspondence from Target, asking users for more information than they would typically be asked to enter, such as a mother’s maiden name or Social Security number, that hackers could use for identity theft, or to take their credentials and use it for cybercrime.

In more grim news, Target said Friday that it would close eight U.S. stores in May, in locations including Las Vegas, Memphis, Tenn., and Middletown, Ohio.

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