SAN FRANCISCO - The company at the centre of a data heist involving Best Buy, Citigroup, and other major brands said Wednesday that the theft of potentially millions of names and email addresses won't significantly slow its email marketing juggernaut.

Epsilon, a subsidiary of Alliance Data Systems Corp., was the victim of a hacking attack that triggered scores of public warnings this week from major retailers, banks and others.

Epsilon sends more than 40 billion emails a year on behalf of more than 2,500 companies, for things like loyalty rewards programs.

In a statement Wednesday, it reiterated that Social Security and credit card numbers weren't compromised. Epsilon president Bryan Kennedy apologized for the inconvenience and the "phishing" emails that victims are receiving.

The company said that only 2 per cent of its client base was affected and that its email volumes aren't expected to be significantly impacted. Epsilon said the incident should have "minimal if any impact" on Alliance Data's financial performance.

Epsilon is a big moneymaker for Alliance Data, which is based in Plano, Texas. Epsilon turned US$65 million in operating profit last year, and its $613 million in revenue was 22 per cent of Alliance Data's total.