CNN reports that a hacker has gained access to as many as 2.2 million Visa and MasterCard accounts. It says that the two companies announced that the hacker breached the security system of a company that processes credit card transactions on behalf of merchants, Visa and MasterCard.
However it seems none of the accounts have been fraudulently used so far. In any case, both card companies have zero-liability policies, which protect cardholders from being held responsible for unauthorized or fraudulent charges.
The culprit however has still not been identified.