TalkTalk says cyber attack "much smaller" than originally suspected

The telecom group said fewer than 21,000 unique bank account numbers and sort codes and 28,000 obscured credit and debit card details were accessed.

In addition, the company said fewer than 15,000 customer dates of birth and 1.2m customer emails addresses, names and phone numbers were accessed.

TalkTalk said that as previously confirmed, the credit and debit card details cannot be used for financial transactions.

The company said it has shared the affected bank details with the major UK banks so they can take their usual actions to protect customers' accounts in the “highly unlikely” event that a criminal attempts to defraud them.

Chief executive officer Dido Harding said: “Today we can confirm that the scale of attack was much smaller than we originally suspected, but this does not take away from how seriously we take what has happened and our investigation is still on going.”

Earlier on Friday, it emerged that a second teenager has been arrested on suspicion of hacking the details of over 4m TalkTalk customers.

The Metropolitan Police said a 16-year old boy was arrested on Thursday in Feltham, west London, and has been released on bail to a date yet to be confirmed.

Police also confirmed that a search was carried out a residential address in Liverpool.

Earlier this week, police in Northern Ireland arrested a 15-year old boy from County Antrim on suspicion of offences under the Computer Misuse Act. He was released on bail until November.

At 1418 GMT, TalkTalk shares were up 4.9% at 253.30p.