TalkTalk cyber-attack: company unsure how many customers affected

Boss apologises for breach which could have compromised financial details of up to 4 million people, amid speculation of Islamic militant involvement

TalkTalk has said it does not know how many of its 4 million customers have been affected by a "significant and sustained" cyber-attack which could have compromised credit card and bank details.

Dido Harding, the chief executive, apologised to customers for the third cyber-attack affecting the telecommunications firm in the past 12 months but said the breaches were "completely unrelated".