Some companies are warning customers that hackers got into their customer files, accessing names and e-mail addresses.

Kroger was one of the first companies to let customers know about the breach. Three more retailers – Best Buy, Tivo and Walgreens – have also come forward saying their customers were also affected.

All of the companies use the same marketing firm – Epsilon.

Officials said hackers accessed Epsilon’s customer files. The companies use Epsilon to send out e-mails to customers.

Epsilon has said no personally identifiable information is stored in the files – it’s mainly just e-mail addresses. But companies are warning customers to be wary of e-mails asking for personal information.

In an e-mail to customers, Kroger assured shoppers the only information at risk is their names and e-mail addresses, but warned them not to open any e-mails from unknown senders.