A security breach at US grocer Hannaford Bros that compromised around 4.2 million credit and debit card accounts was caused by fraudsters installing malware on servers at all of the retailer’s 300 stores.

Hannaford sent out a letter to Massachusetts regulators late last week. The letter, according to reports, stated that malicious software is to blame for the security breach.

The next major question need to be found out here is how was the malware dropped on their system? A lot of people are looking at this carefully because the company had been certified as meeting PCI (Payment Card Industry) data protection standards.

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