Police have arrested a Newcastle teenager suspected of belonging to the Team Poison hacker group.
In April, Team Poison, which has been linked to more than 1,000 offences, claimed responsibility for hacking into the phone system of Scotland Yard's counter-terrorism unit.
The 17-year-old, the third teenager to be arrested in connection with the attack, is believed to have acted as a spokesman for Team Poison, according to the Telegraph.
A day after the attack in April, two boys aged 16 and 17 were arrested by officers from the Police Central e-Crime Unit (PCeU).
In the latest arrest, police officers seized computer equipment for forensic examination.
The PCeU is leading the investigation into the attack on Scotland Yard's counter-terror hotline in which Team Poison used readily available software to bombard the phone line with calls.
The group hacked into the phone system to eavesdrop and record a conversation between officials discussing the incident. The recordings were later posted on the internet.
Team Poison has also claimed responsibility for distributed denial-of-service (DDoS) attacks against banks in collaboration with Anonymous, another hacktivist group.
Other hacks credited to the group include accessing former Prime Minister Tony Blair's address book and posting status updates on the profile of Facebook founder Mark Zuckerberg.