The company has announced that 21,000 TalkTalk customers bank account details were accessed in a data rupture.
Up to 1.2 million customer email addresses, names and phone numbers were also accessed, as were 28,000 obscured credit and debit card details.
As a teenage youngster from Feltham was being interrogated after he was under arrest by officers inspecting the hack on suspicion of computer misuse, the gauge of the data breach was exposed.
Police also proclaimed they had examined a home in Liverpool over the data breach. From County Antrim in Northern Ireland, a 15-year-old boy was week bailed after he was arrested in association with the alleged data theft.
TalkTalk believed the data called up was “significantly less than eventually suspected”.
“Even though the scale of the attack is considerably smaller than primarily suspected, we still continue to guide customers to be watchful, and to take all necessary precautions probable to protect themselves from con emails and phone calls”, said a spokesman.
The developments come just over a week after TalkTalk revealed data of up to four million of its customers may have been stolen in what was believed to be one of the biggest cyber-attacks ever.
The latest breach, with incidents in August and February resulting in customers’ data being taken, is the third in a wave of data breach affecting TalkTalk in the last eight months.