An 18-year-old man has been arrested on suspicion of blackmail over the TalkTalk hack.
Personal details of thousands of customers were accessed in the cyber attack at the end of last month.
It is the fifth arrest in a Met Police investigation into alleged data theft from the communications company.
Police said the teenager was detained at an address in Llanelli, Wales and remains in custody.
A 15-year-old boy from County Antrim, two 16-year-old boys from Feltham and Norwich and a 20-year-old man from Staffordshire have also been arrested over the hack.
All were questioned on suspicion of Computer Misuse Act offences and were released on bail.
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