Tesco Bank has admitted suffering a breach that led to money being stolen from 20,000 customers' accounts.
The bank, which has more than seven million customers, confirmed on Saturday that around 40,000 accounts saw "suspicious transactions" over the weekend, of which half had money taken.
Benny Higgins, Tesco Bank CEO, said in a statement on the company's website: "Tesco Bank can confirm that, over the weekend, some of its customers’ current accounts have been subject to online criminal activity, in some cases resulting in money being withdrawn fraudulently."
Customers have reported that as much as £2,000 was siphoned from their accounts over the weekend. Many of those affected also complained that they were unable to get through to Tesco on the phone.
As well as suspending online transactions, Tesco Bank has blocked some customers' cards. The company said in a statement to the BBC that it hopes to refund customers within 24 hours.
"As a precautionary measure, we have taken the decision today to temporarily stop online transactions from current accounts. This will only affect current account customers," Higgins said.
"While online transactions will not be available, current account customers will still be able to use their cards for cash withdrawals, chip and PIN payments, and all existing bill payments and direct debits will continue as normal. We are working hard to resume normal service on current accounts as soon as possible."
However, the Financial Conduct Authority said that banks must refund unauthorised payments immediately, unless they have evidence that the customer was at fault or the payment was made more than 13 months ago.
We'll update this story as soon as we hear more.
Claims to have "the most competitive logic density" in the industry
Dell's high-end mobile workstations upgraded with Intel Coffee Lake CPUs
Webstresser admins were also arrested in the UK, Croatia, Canada and Serbia
Security firm claims that 117,638 sites out of 135,035 analysed contain serious security flaws