Samata Ullah of Cardiff in Wales admitted to being a member of the Islamic State terror group, terrorist training, preparing terrorist acts and possessing articles for terrorist purposes.
The Old Bailey court in London sentenced Ullah described by Scotland Yard as "very dangerous" to eight years' imprisonment.
"Ullah was a very dangerous individual. He operated primarily on the internet. I would class him as an internet terrorist," said Metropolitan Police Counter Terror unit Commander Dean Haydon.
Ullah,dubbed the "cufflink terrorist" by British media,was a key member of a group calling itself the 'Cyber Caliphate Army' and gave other members of the ISIS advice on how to communicate using the kind of sophisticated encryption techniques employed by online hackers.
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Prosecutor Brian Altman told the court: "He deployed his not inconsiderable self-taught computer skills to further the cause of terrorism and in particular Islamic State, which we say he not merely professed to belong to but in fact belonged in terms of membership and ideological affiliation, all he did from the relative safety of his bedroom in Cardiff, where he lived alone."
Ullah, who has been diagnosed with autism, had admitted five charges earlier in March and the UK Attorney General accepted his guilty pleas.
He also admitted having a book entitled 'Guided Missiles Fundamentals AFM 52-31' and an electronic version of 'Advances in Missile Guidance, Control and Estimation' for terrorist purposes.
British counter-terrorism police had tracked him down after being passed intelligence by the FBI who had been handed the information from authorities in Kenya, who had arrested another man.