Three dozen loyalty accounts belonging to United Airlines customers saw fraudulent transactions after hackers used login credentials collected from an unknown source.
The Mileage Plus accounts, which are part of United's rewards program, were accessed early last month, said Luke Punzenberger, a United spokesman, on Sunday. The program has about 95 million participants.
Punzenberger said the accounts were accessed using login credentials that came from a third party. He did not have specific information on how the airline determined that.
The login credentials were not obtained as a result of a data breach at United, Punzenberger said. He added that United was not the only company that saw attempts to access accounts using the login credentials.
The accounts were temporarily suspended pending verification by affected customers. United said in an advisory that Mileage Plus numbers, account balances and Premier status were exposed and possibly mailing addresses.
The last four digits of a credit card number may have been exposed if a customer had a card number included in their Mileage Plus profile, United said. The rest of the digits are masked.
Loyalty card programs for the travel industry have been increasingly targeted by hackers, as compromised accounts are easy to cash out. United's MileagePlus program lets customers use accumulated miles for air travel, rental cars, dining and shopping.
The incident was reported last week to California's Office of the Attorney General. California law requires organizations to notify residents if unencrypted personal information may have been acquired by an unauthorized person.
Hackers often try to see if login credentials stolen from one Web service will work on another one. For this reason, security experts recommend that people do not re-use passwords, although that mistake is often made.
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