Major banks in India will either replace or ask users to change the security codes of as many as 3.2 million debit cards in what's emerging as one of the biggest ever breaches of financial data in India. Of the cards, 2.6 million are said to be on the Visa and Master-Cardplatform and 600,000 on the RuPay platform. While State Bank of India (SBI) has decided to reissue debit cards to six lakh customers who had used their cards at suspect networks, other banks are asking customers to change their ATM PIN. They are also blocking international transactions that can be conducted without PIN. The fraudsters were able to steal information by way of malware introduced to Hitachi Payment Services, which provides ATM and point of sale services. Sources said similar attacks had occurred at the National Payments Corporation and HDFC Bank. However, HDFC Bank and NPCI said that they had not experienced any specific ransom malware threat. Axis Bank has hired EY to investigate the cyber attack that it had experienced.