British mobile phone retailer Carphone Warehouse last week detected a breach that may have leaked personal details of up to 2.4 million customers.
Along with names, addresses, birthdates, and bank details, the hackers appear to have gotten away with encrypted credit card data for up to 90,000 customers.
"We took immediate action to secure these systems and launched an investigation with a leading cyber-security firm to determine exactly what data was affected," the company's FAQ said. "We have also put in place additional security measures to prevent further attacks."
Discovered on Aug. 5, the breach affected a division of Carphone Warehouse that operates the websites OneStopPhoneShop, e2save, and Mobiles.co.uk; it also provides services to iD Mobile, TalkTalk Mobile, Talk Mobile, and certain Carphone Warehouse clients.
"We and our partners are contacting all those customers who may have been affected to inform them of the breach and to give them advice to reduce any risk and minimize inconvenience," the company said.
There is no word yet on the hackers' identities or their method of attack, which Carphone Warehouse called "sophisticated."
Folks who may have been affected are encouraged to contact their bank and credit card company, keep a close eye on account statements, be wary of anyone asking for personal information or passwords, and check your credit rating online.
As of the weekend, Carphone Warehouse reported no evidence of user information being sold or misused.
"This … is part of the reality of the modern world," the FAQ page said. "Our priority is reducing risk and inconvenience for customers and continuing to build ever stronger defenses."
Customer data for associated retailers and brands Currys, PC World, Dixons Travel, and KnowHow is held on separate systems, and was not accessed.