NEW YORK (CNNMoney) -- A data breach at a payments processing firm has potentially compromised credit and debit card information from all of the major card brands, representatives from MasterCard and Visa said on Friday.News of the breach was first reported by the widely read security blog Krebs on Security. That article said the breach was "massive," and could involve more than 10 million card numbers.The Wall Street Journal followed up with an article saying that processor Global Payments is the vendor that was breached. Global Payments shares fell 9% before trade was halted.A representative of Global Payments did not immediately respond to a request for comment. The extent of the breach, and what kind of information was compromised, has not been confirmed."I've spoken with folks in the card business who are seeing signs of this breach mushroom," Gartner analyst Avivah Litan wrote Friday in a blog post.Her sources say the hackers have begun using some of the card data they stole, Litan added.MasterCard said it has alerted payment card issuers "regarding certain MasterCard accounts that are potentially at risk."The company also said the breach is the subject of an ongoing forensic review by an independent data security organization.