A cyber criminal who took part in a £77 million hack on mobile network TalkTalk and blackmailed former chief executive Dido Harding has been locked up for four years.
Daniel Kelley, from Llanelli, turned to "black hat" hacking when he failed to get the GCSE grades to get on to a computer course.
He hacked the college "out of spite" before targeting companies in Canada, Australia and the UK - including the Telecommunications giant which has four million customers.
The 22-year-old, who has Asperger's syndrome, pleaded guilty to 11 hacking-related offences in 2016.
Judge Mark Dennis sentenced him at the Old Bailey to four years' detention in a young offenders institution.
Judge Dennis said Kelley hacked computers "for his own personal gratification" regardless of the damage caused.
He went on to blackmail company bosses, revealing a "cruel and calculating side to his character", he said.
Kelley caused "stress and anxiety" to his victims as well as harm to their businesses, with the total cost to TalkTalk from multiple hackers estimated at £77 million.
Between September 2013 and November 2015, he engaged in a wide range of hacking activities, using stolen information to blackmail individuals and companies.
Despite attempts at anonymity, his crimes were revealed in his online activities.
In September 2012, he boasted on Skype that he was "involved with black hat activities and I can ddos (Distributed Denial of Service)" in reference to malicious hacking.
He hacked into TalkTalk and blackmailed Baroness Harding of Winscombe and five other executives for Bitcoin, the court heard.
Kelley's activities contributed to TalkTalk losses of tens of millions of pounds, while smaller firms he targeted were forced to spend hundreds of thousands of pounds to mitigate the damage.
The court heard he received £4,400 worth of Bitcoins through all his blackmail attempts, having made demands for more than £115,000.