A second boy has been arrested in connection with the alleged TalkTalk cyber attack, the Metropolitan Police said.
The 16-year-old, from Feltham in west London, was held on suspicion of computer misuse after a search of his home yesterday.
The teenager has been bailed to a date yet to be confirmed.
A 15-year-old boy from County Antrim in Northern Ireland was arrested on Monday in connection with the alleged data theft. He was bailed until a date in November.
The investigation is being carried out by the Met's cyber crime unit, the PSNI's cyber crime centre and the National Crime Agency.
The latest breach is the third in a spate of cyber attacks affecting TalkTalk in the last eight months, with incidents in August and February resulting in customers' data being taken.