In April, we reported that Global Payments, the company that processes credit card transactions for Visa and MasterCard, had been hacked and that approximately 1.5 million users’ credit card information had been compromised. Recent reports indicate that the situation could be worse.

According to Krebs on Security, Global Payments’ system could have been penetrated by hackers as far back as June 2011. In March, Visa and MasterCard issued two alerts, within a week of each other, to card-issuing banks, warning them about the breach. Not long afterward, the Internet was abuzz with the late-breaking news. Since then, Krebs on Security reports, “Visa and MasterCard have issued at least seven updates, warning of additional compromised cards and pushing the window of vulnerability at Global Payments back further each time.”

What does this mean for Visa and MasterCard users? Well, for one thing, it means that the number of compromised accounts could be greater than the originally reported 1.5 million users, though Global Payments insists that the original estimate is correct.

Small- and medium-business owners who use Visa or MasterCard for business might want to keep an eye out for fraudulent activity on their own cards and warn their clients about the possibility that they, too, could be at risk. Where the hack originated remains a mystery. Probably the best thing to do right now is to simply cancel old Visa and MasterCard credit cards and start over with new ones.