Nationwide arts and crafts chain Michaels Stores Inc. said today that two separate eight-month-long security breaches at its stores last year may have exposed as many as 3 million customer credit and debit cards.

The disclosure, made jointly in a press release posted online and in a statement on the company’s Web site, offers the first real details about the breach since the incident was first disclosed by KrebsOnSecurity on January 25, 2014.

The statements by Irving, Texas-based Michaels suggest that the two independent security firms it hired to investigate the break-ins initially found nothing.

“After weeks of analysis, the Company discovered evidence confirming that systems of Michaels stores in the United States and its subsidiary, Aaron Brothers, were attacked by criminals using highly sophisticated malware that had not been encountered previously by either of the security firms,” the statement reads.

The Michaels breach first came to light just weeks after retail giant Target Corp. said that cyber thieves planted malware on cash registers at its stores across the nation, stealing more than 40 million credit and debit card numbers between Nov. 27 and Dec. 15, 2013. That malware was designed to siphon card data when customers swiped their cards at the cash register.

According to Michaels, the affected systems contained certain payment card information, such as payment card number and expiration date, about both Michaels and Aaron Brothers customers. The company says there is no evidence that other customer personal information, such as name, address or debit card PIN, was at risk in connection with this issue.

The company’s statement says the attack on Michaels’ targeted “a limited portion of the point-of-sale systems at a varying number of stores between May 8, 2013 and January 27, 2014.”

“Only a small percentage of payment cards used in the affected stores during the times of exposure were impacted by this issue,” the statement continues. “The analysis conducted by the security firms and the Company shows that approximately 2.6 million cards may have been impacted, which represents about 7% of payment cards used at Michaels stores in the U.S. during the relevant time period. The locations and potential dates of exposure for each affected Michaels store are listed on www.michaels.com.”

Regarding Aaron Brothers, Michaels Stores said it has confirmed that between June 26, 2013 and February 27, 2014, 54 Aaron Brothers stores were affected by this malware, noting that the locations for each affected Aaron Brothers store are listed on www.aaronbrothers.com.

“The Company estimates that approximately 400,000 cards were potentially impacted during this period. The Company has received a limited number of reports from the payment card brands and banks of fraudulent use of payment cards potentially connected to Michaels or Aaron Brothers.”

This incident marks the second time in three years that Michaels Stores has wrestled with a widespread compromise of its payment card systems. In May 2011, Michaels disclosed that crooks had physically tampered with some point-of-sale devices at store registers in some Chicago locations, although further investigation revealed compromised POS devices in stores across the country, from Washington, D.C. to the West Coast.

Michaels says that while the Company has received limited reports of fraud, it is offering identity protection, credit monitoring and fraud assistance services through AllClear ID to affected Michaels and Aaron Brothers customers in the U.S. for 12 months at no cost to them. Details of the services and additional information related to the ongoing investigation are available on the Michaels and Aaron Brothers websites at www.michaels.com and www.aaronbrothers.com.

Incidentally, credit monitoring services will do nothing to protect consumers from fraud on existing financial accounts — such as credit and debit cards — and they’re not great at stopping new account fraud committed in your name. The most you can hope for with these services is that they alert you as quickly as possible after identity thieves have opened or attempted to open new accounts in your name.

As I noted in a recent story about the credit monitoring industry, the offering of these services has become the de facto public response for companies that experience a data breach, whether or not that breach resulted in the loss of personal information that could lead to actual identity theft (as opposed to mere credit card fraud). For more information about the limitations of credit monitoring services and more proactive steps that you can take to better protect your identity and credit file, check out this story.

Tags: Aaron Brothers breach, AllClearID, michaels breach