NEW DELHI/MUMBAI, Oct. 21 -- Some 3.2 million debit cards issued by India's biggest banks have been exposed to a malware-induced security breakdown, but the actual number could be much more.

Most of these cards belong to State Bank of India (SBI), HDFC Bank, Yes Bank and ICICI Bank.

Of the 3.2 million, 2.6 million are said to be the Visa and MasterCard platform, and 600,000 on the RuPay platform.

Top officials of the National Payments Corp of India (NPCI) said the investigation into the malware attack on Hitachi Payment Services is in its initial stages, so the extent of the danger is yet to be ascertained.

According to reports, the breach is said to have originated in malware introduced Hitachi Payment Services system. This leads to da...