e-mail address theft

With the possible theft of millions of email addresses from an advertising company, several large companies have started warning customers to anticipate fraudulent emails that make an effort to coax account login information from them.

Companies behind such brands as Chase, Citi and Best Buy said over the weekend that hackers may have learned their email addresses because of a security breach at a Dallas-based company called Epsilon that manages email communications.

The email addresses could possibly be used to target spam. It's also a normal tactic among online fraudsters to transmit emails to random people, purporting to be from a large bank and asking them to login in at a site that appears like the bank's site. Instead, the fraudulent site captures their login information and uses it to access the real account.

The data breach could make these so-called "phishing" attacks more efficient, by allowing the fraudsters to target individuals who actually have an account with the bank.

David Jevans, chairman and founder of the non-profit Anti-Phishing Working Group, said criminals are already leaving indiscriminate phishing towards more intelligent attacks known as "spear phishing," which depend on having more intimate knowledge of the victims.

"This data breach is going to facilitate that in a big way. Now they know which institution people bank with, they know their name and they have their email address," said Jevans, who is also the CEO of security company IronKey Inc.

"You're not going to see typical phishing where 90 percent of it ends up in spam traps and is easily detected. This is likely to be highly targeted," he added. On the list of affected are financial-service companies such as Capital One Financial Corp., Barclays Bank, U.S. Bancorp, Citigroup Inc., JPMorgan Chase & Co. and Ameriprise Financial Inc. and retailers including Best Buy Co., TiVo Inc., Walgreen Co. and Kroger Co.

The College Board, the not-for-profit organization that runs the SATs, also warned that a hacker may have obtained student email addresses.

Walt Disney Co.'s travel subsidiary, Disney Destinations, sent emails warning customers on Sunday. Hotel chain Marriott International Inc. issued a similar warning.