The former leader of the hacking group known as TeaMp0isoN faces jail after pleading guilty to stealing Tony Blair's personal details from an aide's email account, and making 100 prank calls to the UK's anti-terrorism hotline.
Junaid Hussain, also known as TriCk, admitted hacking into the email account of Katy Kay, a former special adviser to Blair.
He also admitted making information taken from Blair's emails, including phone numbers and contact information, public.
He also told Southwark Crown Court that he attacked the MI6 hotline, admitting conspiracy and computer charges.
According to the Sun, TriCk's lawyer argued the hacks were just a prank, but the judge warned he could face prison.
INTERVIEW: Huffington Post Speaks To MI6 Hacker TriCk
Police are said to be still investigating other attacks carried out by Team Poison.
In an interview with the Huffington Post earlier this year, Hussain said that he was sure he would not be caught.
"Don't fear us," he said. "We are not the oppressors - we don't attack innocent people or hack random people, we are against that. 'With great power comes great responsibility' - and we understand that.
"TeaMp0isoN is based on trust, we have all known each other for years, we all have the same goals and motives - to be a "successful" hacktivist team you must have a circle of trust.
"We can go back to being underground and you'd never hear of us ever again, but we do this for the cause and to make a change. We don't care about the fame, or being 'power hungry', the only power we seek is to change stuff or to embarrass the victim."