A 15-year-old boy has been arrested in Northern Ireland in connection with the TalkTalk hacking attack, Scotland Yard has said.
Metropolitan Police said a house had been searched in County Antrim on Monday afternoon at about 16:20 GMT.
The boy was arrested on suspicion of Computer Misuse Act offences.
He has been taken into custody at Antrim police station and is being questioned by detectives from the Police Service of Northern Ireland.
A search of the address is ongoing and inquiries continue.
A police statement said this was a joint investigation involving the Police Service of Northern Ireland (PSNI), and detectives from the Metropolitan Police Cyber Crime Unit (MPCCU).
News that the TalkTalk website had been hit by a "significant and sustained cyber-attack" broke last week.
The phone and broadband provider, which has over four million UK customers, said banking details and personal information could have been accessed.
A criminal investigation was launched on Thursday.
The company said it did not know how much of their customer information had been encrypted.
At the weekend, TalkTalk's chief executive said the attack was "smaller" than originally thought.
Dido Harding said any credit card details taken would have been partial and the information may not have been enough to withdraw money "on its own".
Card details accessed were incomplete - with many numbers appearing as an x - and "not usable" for financial transactions, it added.
Business leaders have called for urgent action to tackle cyber crime in the wake of the TalkTalk attack.
On Monday, MPs said an inquiry would be launched into the cyber-attack that could have put customers' details at risk.
Culture minister Ed Vaizey told the House of Commons the government was not against compulsory encryption for firms holding customer data.
Shares in the telecoms company fell more than 12% in Monday trading, extending its losses from last week, when news of the attack first emerged.