The BBC reports Scotland Yard saying that a 15-year-old boy has been arrested in Northern Ireland on suspicion of Computer Misuse Act offences relating to the TalkTalk hack.
The Metropolitan Police confirmed an ongoing house search in County Antrim begun on Monday afternoon and that the boy has been taken into custody at a police station in Antrim.
An official statement says this is a joint investigation involving the Police Service of Northern Ireland (PSNI), and detectives from the Metropolitan Police Cyber Crime Unit (MPCCU).
Shares in firm fell 12 percent on Monday.
TalkTalk executives are to be summoned before MPs to explain how the hacker(s) stole data from up to four million customers; the inquiry into the hack and data protection will be launched by Jesse Norman, chair of the Culture, Media and Sport Select Committee.
Culture minister Ed Vaizey also told the House of Commons the government was not against compulsory encryption for firms holding customer data.
More to follow.