UK police arrested a third suspect on Saturday relating to the breach at communications provider TalkTalk, which said the amount of data exposed is less than initially thought.
A 20-year-old man was arrested after police executed a search warrant at an address in south Staffordshire, the Metropolitan Police said Sunday.
The man, who was not identified, was arrested on suspicion of violations of the Computer Misuse Act and was later bailed.
UK police arrested a 15-year-old boy in County Antrim, Northern Ireland, on Oct. 26, and a 16-year-old boy in Feltham, England, on Thursday. Both boys have been bailed.
TalkTalk's website was breached on Oct. 21, exposing customer names, addresses, birth dates, email addresses, phone numbers, account information, payment card and bank account details.
In a video, TalkTalk CEO Dido Harding said "the extent of the data accessed is significantly less than originally suspected."
Less than 21,000 unique bank account numbers and sort codes, 28,000 credit and debit card details, 15,000 customer birth dates and 1.2 million email addresses, names and phone numbers were exposed, according to an advisory.
For the payment card details, the middle six digits were removed, TalkTalk said. That would make the numbers less useful for cybercriminals. U.K. banks have also been notified of the leaked bank details in order to closely watch those accounts for fraud.
TalkTalk has maintained that criminals would need further information make use of people's bank account numbers and sort codes for fraud.
Harding said the investigation into the attack continues with the Metropolitan Police's Cyber Crime Unit.
The company is offering a year's worth of free credit monitoring to those affected through Noddle. It also said it will waive the termination fee charged for leaving TalkTalk while under contract if a customer can prove a fraudulent transaction occurred after the data breach.
The breach marked the third one for TalkTalk this year, which prompted criticism that the company hasn't done enough to shore up its cybersecurity defenses.