The BBC are reporting that he was arrested on suspicion of Computer Misuse Act offences after detectives searched a Feltham address, and later bailed, Scotland Yard said.
On Tuesday, a 15-year-old boy arrested in Northern Ireland in connection with the attack was released on bail pending further inquiries.
The TalkTalk website was hit by a “significant” cyber-attack” last week.
The phone and broadband provider, which has over four million UK customers, said banking details and personal information could have been accessed.
Officers have also searched a residential address in Liverpool, the Metropolitan Police said.
