The insecure wireless network at a Marshalls discount clothing store near St. Paul, Minn. may have allowed hi-tech attackers to gain a beachhead in retail giant TJX Companies' computer network, resulting in the theft of information on at least 45.6 million credit and debit cards, the Wall Street Journal reported on Friday.

While TJX's other systems were upgraded to Wi-Fi Protected Access (WPA), the Marshalls store's wireless network connecting credit-card processing hardware to the company's server was not, investigators working on the case told the WSJ (subscription required).

"It was as easy as breaking into a house through a side window that was wide open," said a person familiar with TJX's internal probe, according to the WSJ article.

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