NEW DELHI (AP) — Indian banks are scrambling to contain the damage after more than 3.2 million debit cards may have been hacked.

Several banks, including the government-run State Bank of India, advised customers Friday to change their personal identification numbers. The banks have recalled thousands of debit cards and blocked others that they fear may have been hacked.

The breach is thought to have been caused by malware on an ATM network.

Finance Minister Arun Jaitely said Friday the goverment was investigating how the security breach occurred.

The National Payments Corporation of India that controls all retail payments systems in India said banks had received complaints from customers that their cards had been used fraudulently in China and the United States.