The boy is the fourth to be arrested in the inquiry into the hack, which saw TalkTalk data filched in the attack.
TalkTalk claims that the hack was much smaller than it had originally thought.
All four young men have been arrested and released on bail while police inquiries continue.
Meanwhile British MPs are setting up their own inquiry into TalkTalk.
The Culture, Media and Sport Committee wants to investigate how firms like TalkTalk store customer data.