Major banks and credit-card issuers Capital One, Barclays Bank, U.S. Bancorp and Citigroup have joined the list of companies warning customers that hackers may have learned their email addresses.

The companies all use a Dallas-based company called Epsilon to manage their emails to customers. Epsilon said Friday that its system had been breached, exposing email addresses and customer names but no other personal information.

The hackers also gained access to the email addresses of customers of JPMorgan Chase & Co., Best Buy Co., TiVo Inc., Walgreen Co. and Kroger Co.

The affected companies said the email addresses could be used to target "phishing" attacks -- seemingly legitimate emails that try to coax account login information from victims.

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