Thousands of Tesco Bank current account customers appear to have been targeted by fraudsters, with some saying they have lost hundreds of pounds.
Customers have complained about money being withdrawn without permission, cards being blocked and long delays to get through to the bank on the phone.
The bank said its anti-fraud systems had identified "suspicious activity" on some customer accounts.
It said the customers affected were in their "thousands but less than 10,000".
By Sunday evening, Tesco Bank said it had spoken to the majority of those customers affected and any stolen money would be refunded from Monday onwards and "within 24 business hours".
Some cards had been immediately blocked as a precautionary measure, but affected customers were still be able to use online banking and carry out chip and pin transactions, the company said.
It said customers should contact the bank if they had any concerns, but added: "We can reassure our customers that they will not lose out as a result
Tesco Bank customers lose money to 'fraudsters' - BBC News
Customers have complained about money being withdrawn without permission, cards being blocked and long delays to get through to the bank on the phone.
The bank said its anti-fraud systems had identified "suspicious activity" on some customer accounts.
It said the customers affected were in their "thousands but less than 10,000".
By Sunday evening, Tesco Bank said it had spoken to the majority of those customers affected and any stolen money would be refunded from Monday onwards and "within 24 business hours".
Some cards had been immediately blocked as a precautionary measure, but affected customers were still be able to use online banking and carry out chip and pin transactions, the company said.
It said customers should contact the bank if they had any concerns, but added: "We can reassure our customers that they will not lose out as a result
Tesco Bank customers lose money to 'fraudsters' - BBC News
