LONDON (Reuters) - Britain's TalkTalk said a "significant and sustained" cyber attack on its website could involve the theft of private data from all of the broadband supplier's more than 4 million customers. "Investigation is ongoing but unfortunately there is a chance that some of the following data has been compromised: names, addresses, date of birth, phone numbers, email addresses, TalkTalk account information, credit card details and/or bank details," the company said in a statement late on Thursday.
Chief Executive Dido Harding said it was too early to know exactly what data had been stolen, but the company wanted to contact all customers as quickly as possible so they could monitor their accounts.
"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," she told the BBC.
Shares in the company were down 3.9 percent to 258 pence in early trade on Friday.
The group has suffered security breaches before, including in August when servers owned by Carphone Warehouse, the retailer which founded TalkTalk, were attacked, potentially affecting TalkTalk's mobile customers.
A spokeswoman said Wednesday's attack was the first time TalkTalk's own servers had been subjected to a sustained external attack.
(Reporting by Paul Sandle in London and Rama Venkat Raman in Bengaluru; editing by Jason Neely)