A third person has been arrested by police investigating the cyber attack on telecoms firm TalkTalk.
A 20-year-old man was detained at an address in Staffordshire today after officers executed a search warrant, Scotland Yard said.
He is being held on suspicion of offences under the Computer Misuse Act and remains in custody at a local police station.
Two teenagers have previously been arrested in connection with the alleged data theft.
A 16-year-old boy, from Feltham in west London, was held on suspicion of computer misuse after a search of his home on Thursday.
The teenager has been bailed to a date yet to be confirmed.
Meanwhile, a 15-year-old boy, from County Antrim in Northern Ireland, was arrested on Monday and was bailed until a date in November.
The investigation is being carried out by the Metropolitan Police's cyber crime unit, the Police Service of Northern Ireland's cyber crime centre and the National Crime Agency.
The latest breach is the third in a spate of cyber incidents affecting TalkTalk in the last year.