Epsilon, the world's largest permission-based email marketing Services Company that serves TiVo users and many more, reported a breach in its security Friday and the list of companies affected keeps on growing, Mashable reported.

The security breach has reportedly affected more than 2,500 clients including Best Buy, TiVo, Walgreens, Capital One, JP Morgan and Citigroup.

While most of these companies are understandably mum on how many customers might be at risk, it's not inconceivable that millions of users' information may have been accessed by an unauthorized party, the report further added.

However, Epsilon issued a statement on its website, stating that, an incident was detected where a subset* of Epsilon clients' customer data were exposed by an unauthorized entry into Epsilon's email system. The information that was obtained was limited to email addresses and/or customer names only. A rigorous assessment determined that no other personal identifiable information associated with those names was at risk. A full investigation is currently underway.

The complete list of companies whose customers' data has been accessed is unknown.

The list of the few companies named so far is below:

  • Target
  • Best Buy
  • Walgreen's
  • Capital One
  • TiVo
  • JP Morgan Chase & Co.
  • Kroger
  • US Bank
  • Citi
  • McKinsey & Company
  • Ritz-Carlton Rewards
  • Marriott Rewards
  • New York & Company
  • Brookstone
  • The College Board
  • Home Shopping Network (HSN)
  • LL Bean
  • Disney Destinations
  • Barclays Bank of Delaware