Data theft: Top 5 most expensive data breaches

1. (tie) Epsilon - to be determined

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    People line up early in the morning to purchase the RIM PlayBook at a Best Buy store in Toronto, April 19, 2011. Best Buy was a customer of Epsilon, the e-mail marketing firm that lost millions of e-mail addresses and names to cyber criminals in March.
    Mark Blinch / Reuters / File
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In March 2011, hackers stole millions of names and e-mail addresses from the Dallas-based marketing firm. Epsilon handles e-mail lists for major retailers and banks like Best Buy, JPMorgan, TiVo, Walgreen, and Kroger. A study by CyberFactors, a cyber risk analytics company, estimates that the breach could cost between $225 million and $4 billion, depending on what happens with the stolen data, Business Wire reports. Mr. Ponemon offers a lower estimate: at least $100 million, with most of the lost costs going toward losing customers due to a damaged reputation. Ponemon says that because the stolen data was e-mail information, the costs won't be as high as if financial information had been stolen.

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