Dixons Carphone (DC.L) have been subject to a cyber attack that may affect 2.4 million of its customers, the retailer announced on Saturday.
The electrical and mobile phone company said that it had learned of the data breach on Aug. 5 and had taken immediate action.
The affected part of the company includes the OneStopPhoneShop.com, e2save.com and Mobiles.co.uk websites, as well as around 400,000 TalkTalk customers.
Up to 90,000 customers may also have had their encrypted credit card details accessed, it said in a statement.
Sebastian James, chief executive of Dixons Carphone, said: “We are, of course, informing anyone that may have been affected, and have put in place additional security measures.
“We take the security of customer data extremely seriously, and we are very sorry that people have been affected by this attack on our systems.”