The teen was taken into custody in Northern Ireland.
The 15-year-old boy was taken into custody around 4 PM local time on suspicion of Computer Misuse Act offenses, Metropolitan Police said in a statement. He was brought to a County Antrim police station where he will later be interviewed, the Metropolitan Police said.
The arrest comes after TalkTalk revealed it had been hacked on Thursday of last week, saying an "individual or a group purporting to be the hacker" had demanded £80,000, or about $122,000 in Bitcoin as ransom for user information that was stolen.
A hacker claiming to represent previously defunct collective LulzSec took responsibility for the DDoS attack on TalkTalk last week, which works by flooding the target's system with traffic, but not for the stolen user information or extortion attacks. It is not entirely clear which attack the arrest relates to: the hack that resulted in the theft of customer data, or the DDoS that affected the site. It's also unclear if the hacker who was arrested is the same person who claimed responsibility for the DDoS attack to Motherboard.
TalkTalk issued a statement about the development through the Metropolitan Police.
"We know this has been a worrying time for customers and we are grateful for the swift response and hard work of the police," TalkTalk said. "We will continue to assist with the ongoing investigation."