TALK TALK breaking news
Millions of card and bank details could have been compromised after a "significant and sustained" attack on the TalkTalk website.
In a statement the firm said: "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 Metropolitan Police's Cyber Crime Unit has launched an investigation and "leading" specialists are on the case.
The company's four million customers are being urged to check their accounts for any suspicious activity.
"We take any threat to the security of our customers’ data extremely seriously and we are taking all the necessary steps to understand what has happened here," said TalkTalk boss Didi Harding.
"As a precaution, we are contacting all our customers straight away with information, support and advice around yesterday’s attack.”
The company's website is currently down, with people being asked to call up to service their account.
Before the TalkTalk statement, some customers had been reporting problems with webmail and broadband over the last 24 hours.