Prompting pre-Diwali panic among customers, an estimated 3.2 million debit cards of various banks are believed to have been “hacked” following a suspected security breach.

Investigations have begun into the causes behind the security risks. Several banks, including the State Bank Of India (SBI), have already started blocking their customers’ debit cards and re-issuing fresh ones free of cost.

An estimated three million debit cards issued by various public or private banks are said to be affected by a potential data breach.

Debit or credit cards are prone to security issues when unauthorised parties gain access to the confidential data embedded on them, even as they are being swiped in an automatic teller machine (ATM).

In the current scenario, the SBI alone has blocked more than 600,000 debit cards while assuring that the malware-related security breach was reportedly detected in the non-SBI ATM network.

The move has been undertaken to ensure that customers’ confidential personal data is not compromised while debit or credit cards are swiped for various transactions.

One of the card network companies, MasterCard said on Thursday that its “own systems have not been breached”.

“We are working on the investigations with the regulators, issuers, acquirers, global and local law enforcement agencies and third party payment networks to assess the current situation,” a MasterCard spokesperson said.

It has advised the consumers to review their account statements and activity, and if any unusual or fraudulent transactions are suspected, they should contact the concerned bank for more assistance.

Anxious customers have started enquiring with their banks over the seriousness of the problem, whether their personal data has leaked out and if that could lead to financial implications, especially with Diwali round the corner.

On Wednesday evening, the SBI said it has blocked cards of certain customers identified by the networks as a precautionary measure, though it did not reveal the exact number of cardholders who would be hit.

The SBI emphasised that its own systems have absolutely not been compromised and existing cardholders are not at any risk and can continue to use their cards as usual.

According to banking circles, several other banks have also experienced similar problems as a few ATMs have been hit by a malware which has a high potential to compromise customers data.

Official figures indicate that the SBI has over 200 million active debit cards, besides 47.5 million others of its associate banks.

In early September, the National Payments Corporation of India (NPCI), Mumbai, which controls all the retail payments systems in the country, had made it clear that there “is no compromise at NPCI and our systems are fully safe and secure.”

NPCI handles over 25 million transactions daily, including RuPay cards, of which more than 290 million are currently in circulation.