Ransom call to Talk Talk after cyber attack

British broadband provider Talk Talk said on Friday it had received a ransom demand from an unidentified party claiming responsibility for a cyber attack that could have led to the theft of personal data from its more than 4 million customers.

The data could include credit card and bank details, and if the theft is confirmed by a police investigation it would be one of Britain’s biggest online security breaches.

“We have been contacted by, I don’t know whether it is an individual or a group, purporting to be the hacker,” Talk Talk CEO Dido Harding told the BBC, without giving details.

Jens Monrad, a Copenhagen- based security expert for US cyber defence firm Fire Eye, also told Reuters that samples of financial data which appeared to come from Talk Talk customers had been spotted for sale in cybercriminal forums on the so- called dark web.

A Talk Talk spokesperson declined to comment, citing the ongoing police investigation.

The attack is potentially one of the largest and most damaging to hit a British company, and follows dozens of high- profile cases targeting retailers and banks in North America.

The details of millions of customers of infidelity website Ashley Madison were leaked in August after a massive cyber assault, while Sony Corp’s film studios were hit last year.

Talk Talk said late on Thursday there was a chance names, addresses, dates of birth, phone numbers, email addresses, Talk Talk account information, credit card details and/ or bank details had been accessed.

“Potentially this could affect all of our customers. I don’t know for certain, which is why we are taking the precaution of reaching out to everyone,” Harding told the BBC. The attack is the third data breach to hit Talk Talk this year, and experts said it would damage the reputation of the company, which competes with bigger rivals BT, Virgin Media and Sky in the broadband market.

“Their brand will be damaged and their customers will say it is the final straw,” said computer security expert Graham Cluley.

Shares in Talk Talk, which had fallen 7 per cent since the group’s websites went down on Wednesday, fell as much as 8.5 percent on Friday.