Computer hackers gained access to the email addresses of customers of several large US banks and other companies in a potentially huge data breach at US online marketing firm Epsilon.

Banking firms Citigroup, JPMorgan Chase and Capital One, retailers Best Buy and Kroger and home entertainment provider TiVo were among those informed by Epsilon that some customer email addresses had been compromised.

Epsilon, a marketing vendor used by 2,500 companies around the world to send more than 40 billion emails a year, said the hackers obtained email addresses and customer names but no other information.

"A subset of Epsilon clients' customer data were exposed by an unauthorised entry into Epsilon's email system," the company said in a brief statement.

"The information that was obtained was limited to email addresses and/or customer names only," it said. "A rigorous assessment determined that no other personal identifiable information associated with those names was at risk."

Epsilon said it detected the breach on March 30 and that an investigation is underway.

Citi said it had been notified by Epsilon that "the information that was obtained was limited to the names and/or e-mail addresses of some customers of Citi's North American credit card businesses, and no account information or other information was compromised."

Capital One also said it had been told the compromised files did not include any personally identifiable or customer financial information.

JPMorgan Chase said it had been "advised by Epsilon that the files that were accessed did not include any customer financial information, but are actively investigating to confirm this."

Online travel site TripAdvisor said last month that hackers stole a portion of its email list of its members.