Shares in British broadband provider TalkTalk were hit as it said it had received a ransom demand from an unidentified party claiming responsibility for a cyber attack that may have led to the theft of personal data from its more than four million customers.

Its shares were down by more than 8 per cent at one stage, before closing down by some 4 per cent.

The data could include credit card and bank details. 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,” TalkTalk chief executive Dido Harding told the BBC.

She said the demand for payment came by email into her corporate account. – (Reuters)