Sanjeev Moghe, head of cards and payments at the city-based lender, said starting Tuesday evening, customers witnessed unauthorised transactions where they received transaction alerts on certain low-value purchases being carried out at some e-commerce sites.

There has been “no data breach” at the bank’s end, Moghe said, asserting that the scale of such transactions is very limited and customers’ data is safe and secure.

Amid growing social media chatter about such unauthorised transactions going through, Moghe said the bank’s internal mechanisms stopped some transactions but added that many customers have been impacted.

The bank witnessed spends of about ₹500 crore per day by its credit card customers, Moghe said, adding that when compared with it, the extent of such transactions has been “very small”.

Asked for more details, he said it is a small fraction of the overall spends and added that “we are speaking about thousands and lakhs”. He also hinted that such incidents happened for a day, and have stopped.

Fraudsters gained access to a few card numbers and matched it with the expiry dates to carry out the unauthorised transactions, he said, explaining that as these are international transactions, they can go through without any second factor authentication like a one time password over SMS or even the CVV number.

To a query on how the data can be sourced by the fraudsters, he said the first six digits in a 16-digit number are bank-specific, and added that the card numbers can be picked up when the card is given for payments at petrol pumps or restaurants.

Asked if other banks have also experienced similar instances as their customers’ credit card numbers can also get picked up in a similar way, Moghe said he is not immediately aware about the same.

Axis Bank is replacing the credit cards for the impacted customers, and charging back the debited amount, Moghe said, adding that this is not a hit for the lender.

The Reserve Bank has been informed about the incidents and the bank will have to look at strategies like audits to avoid such incidents in the future, he said.

The Axis Bank scrip closed 0.50 per cent down at ₹1,048.30 a piece on the BSE on Thursday as against gains of 0.90 per cent on the benchmark.