Retailer Dixons Carphone has become the latest victim of a cyber attack after revealing 5.9 million customer bank card details and 1.2 million personal data records were hacked.
The group said that, while 5.8 million of the payment cards targeted were protected by chip and pin, around 105,000 non-EU cards without chip and pin protection were compromised.
Dixons Carphone, which owns Currys PC World, said relevant card companies had been notified, but added that there was no evidence of fraud on the cards as a result of the incident.
It added that its investigation had also found that hackers accessed non-financial personal data - such as name, address or email details - for 1.2 million customer records.
The group is contacting all those affected, but sought to assure customers it had no evidence that this had resulted in fraud at this stage.
It said it had called in cyber experts and added extra security to its systems following the breach, while also since calling in the police and relevant authorities.
Dixons Carphone chief executive Alex Baldock admitted the group had "fallen short" of its responsibility to protect customer data.
He said: "We are extremely disappointed and sorry for any upset this may cause.
"The protection of our data has to be at the heart of our business, and we've fallen short here.
"We've taken action to close off this unauthorised access and, though we have currently no evidence of fraud as a result of these incidents, we are taking this extremely seriously."