Dec. 21, 2013 -- The CEO of Target apologized to the public for slower call center and website access and is now offering a 10 percent discount to all customers after a massive data breach left information of about 40 million shoppers vulnerable to thieves.

In his message, Target CEO Gregg Steinhafel said on Friday that the issue of unauthorized access to payment card data at their U.S. stores "has been identified and eliminated," and not all customers who shopped between Black Friday and last week are victims of fraud.

"Most importantly, we want to reassure guests that they will not be held financially responsible for any credit and debit card fraud. And to provide guests with extra assurance, we will be offering free credit monitoring services. We will be in touch with those impacted by this issue soon on how and where to access the service."

Target said that if a customer notices charges they did not make in their credit or debit account, they should contact the company at 1-866-852-8680. Otherwise, customers do not need to call, Target said, adding that the company will never ask a guest for their social security or pin number.

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Steinhafel apologized to guests who tried to reach Target via its website or call center while it faces "unprecedented call volume." To ease the public's perception of Target, Steinhafel is offering a 10 percent in-store discount to customers in a single transaction on Saturday and Sunday.

"It was a crime against Target, our team members, and most importantly, our guests," he said in his statement. "We're in this together, and in that spirit, we are extending a 10 percent discount – the same amount our team members receive – to guests who shop in U.S. stores on Dec. 21 and 22."

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But whether the discount and free credit card monitoring service will ease the nerves of Target shoppers who have already been victims of credit card fraud is yet to be seen.

ABC News has learned that credit card numbers stolen from the recent data breach at Target are now hitting the black market in the form of fake credit cards.

Missy Thompson of Tennessee believed her card was part of the huge breach when she noticed unusual activity on her card.

"I was thinking, I didn't go to Walgreens. I would never spend 250 dollars in Walgreens so, that got my attention," Thompson told ABC News Radio.

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Matt Ferrante, a former secret service agent said once stolen credit cards are harvested, they're "dispersed all over the world and usually distributed through on-line organized crime."

ABC News Radio contributed to this report.