Another suspect picked up in TalkTalk investigation.
Police have made a fourth arrest, of a 16-year-old boy, in connection with the investigation into an alleged data theft from TalkTalk.
He was held on suspicion of Computer Misuse Act offences after officers searched an address in Norwich.
Police have also arrested and bailed a 16-year-old from London, a 15-year-old boy in County Antrim, Northern Ireland, and a man, 20, from Staffordshire.
The TalkTalk website was hit by a “significant” hacking attack last week.
On Friday, the phone and broadband provider confirmed that at most 1.2 million email addresses, names and phone numbers and 21,000 unique bank account numbers and sort codes were accessed in the attack.
It was fewer than originally thought, the firm said.
The company, which has more than four million UK customers, said it would be writing to all affected people to let them know what information had been accessed.
It said that any stolen credit or debit card details were incomplete – and therefore could not be used for financial transactions – but advised customers to remain vigilant against fraud.
The fourth arrest in connection with the attack came after detectives from the Metropolitan Police Cyber Crime Unity and the National Crime Agency executed a search warrant at the Norwich address, the Met said.
The 16-year-old remains in custody at a local police station.