Stolen data may be sold on cyber black market

And while the tens of millions of names and email addresses swiped from online marketing firm Epsilon do not appear to have been used yet for cyber crime, experts said it may just be a matter of time.

Major US banks, hotels, retail outlets and other companies have been warning customers to be wary of fraudulent emails after Epsilon acknowledged last week that hackers had gained access to the Texas-based company's email system.

Epsilon, which provides email services for some 2,500 companies around the world, has said that customer data for about two percent of its total clients was exposed in what it called an "unauthorised entry."

Ed Heffernan, chief executive of Alliance Data Systems Corp.