Millions of consumers in the UK are thought to have had their personal details compromised after a major cyber attack at telecoms provider TalkTalk.
While the company has said it is still too early to know exactly what data has been stolen or how many accounts are affected, it added that the breach has the potential to affect all of its four million customers in the UK.
Information that may have been accessed includes names and addresses, dates of birth, telephone numbers and financial details such as credit card numbers. Not all of this data was encrypted.
Chief executive of TalkTalk Dido Harding told the BBC the attack was first detected on Wednesday afternoon (October 21st) and the firm responded by taking down all its websites and immediately contacting police. Its sales website and 'My account' services remained offline until Friday morning, while its main site has been confirmed as secure again.
This is not the first time that TalkTalk has been targeted by cyber criminals. In February, the company warned customers about scammers who had managed to steal the names and account numbers of thousands of customers. Then in August, it admitted its mobile sales site had also been targeted, leading to the loss of personal data.
Ms Harding said: "Unfortunately cybercrime is the crime of our generation. Can our defences be stronger? Absolutely. Can every company's defences be stronger?"
Some customers have already expressed their anger at the latest breach, and commentators have warned it will have serious consequences for the firm's reputation.
Cybersecurity expert Professor Peter Sommer told the BBC: "Undoubtedly TalkTalk has had significant problems for some time and they simply had to go public now because personal data is available and the Information Commissioner is going to be hard down on them to see why they haven't performed better."
He also noted that while all organisations are facing challenges as the number and sophistication of attacks increase , TalkTalk could be particularly vulnerable as it has been undergoing rapid growth recently.
"Each of those customers wants to do more things and so they have to increase their capacity, but that's an expensive exercise," he added.