BBC article states that DDoS attack preceded data theft.
The head of TalkTalk says she has had an email demanding a ransom from a group purporting to be behind the cyber-attack suffered by the company.
Chief executive Dido Harding said she did not know whether the ransom email was genuine.
The phone and broadband provider said personal and banking details of up to four million customers may have been accessed in the “significant” attack.
The Met Police said the email was “forming part of its investigations”.
Ms Harding told the BBC: “It is hard for me to give you very much detail, but yes, we have been contacted by, I don’t know whether it is an individual or a group, purporting to be the hacker.
“All I can say is that I had personally received a contact from someone purporting – as I say I don’t know whether they are or are not – to be the hacker looking for money.”
‘Worry and concern’
TalkTalk said it was too early to know exactly who had been affected by the attack, which happened on Wednesday.
“I’m very sorry for all the frustration, worry and concern this will inevitably be causing all of our customers,” Ms Harding added.
She said the company was “rushing to communicate with customers” but that it would take 36 to 48 hours to email all of them.
In a statement, the company said that a criminal investigation had been launched on Thursday.
The Metropolitan Police, which is investigating, said no-one had been arrested over Wednesday’s attack but inquiries were ongoing.
TalkTalk said there was a chance that some of the following customer data, not all of which was encrypted, had been accessed:
- Names and addresses
- Dates of birth
- Email addresses
- Telephone numbers
- TalkTalk account information
- Credit card and bank details
In the wake of the news, the company’s share price initially fell to its lowest level since August 2013, but later recovered and by 14:30 BST it was only 2% lower.
Cyber security consultant and former Scotland Yard detective Adrian Culley told BBC Radio 4’s Today programme that a Russian Islamist group had posted online saying it carried out the attack.
He said hackers claiming to be a cyber-jihadi group had posted data which appeared to be TalkTalk customers’ private information – although he stressed their claim was yet to be verified or investigated.