The security of customer data is an increasing source of concernas a new data leak in the US is reported
The company, in a weekend statement, said, "A subset of Epsilon clients' customer data has been exposed by an unauthorised entry into Epsilon's email system".
The data "was limited to email addresses and/or customer names only", said Epsilon.
Brands including Tivo, Best Buy and JPMorgan Chase have told customers of the problem.
Epsilon, one of the planet's biggest email marketing companies, sends out more than 40 billion emails a year on behalf of 2,500 clients. Customers of two per cent of the these clients - around 50 companies - were affected
The problem may not have affected Epsilon's operations in the UK, although Epsilon in the US would not confirm this. One British client Tesco said, "Epsilon have told us these problems are limited to the United States."