'Massive' Data Breach May Have Hit MasterCard, Visa 10M cards may be affected By Matt Cantor, Newser User Posted Mar 30, 2012 10:07 AM CDT 6 comments Comments MasterCard and Visa are both looking into a possible security breach. (AP Photo/Mark Lennihan, file) (Newser) – MasterCard is investigating a feared security breach linked to a credit-card processor in the US, it says; Visa has reportedly launched a similar investigation. While the companies are mum about the extent of the problem, financial insiders tell Krebs on Security it's "massive," potentially involving 10 million cards. MasterCard says it has notified law enforcement as well as issuing banks about "certain MasterCard accounts that are potentially at risk," the Wall Street Journal reports. Visa is also notifying banks, according to Krebs. Banks themselves are trying to track down the processor behind the breach; the compromised cards appear to have been used at New York City-area parking garages, sources tell Krebs. An independent security firm is also on the case, MasterCard says. The data breach occurred between Jan. 21 and Feb. 25, reports Krebs; the site suggests that the info taken could be used to make counterfeit cards.