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.Commenting on what he was doing, he wrote on an online forum: “Oh God, this is so illegal.”The court heard how Kelley was just 16 when he hacked into Coleg Sir Gar out of “spite or revenge”.The DDoS attack caused widespread disruption to students and teachers and also affected the Welsh Government Public Sector network – including schools, councils, hospitals and emergency services.In December 2016, Kelley pleaded guilty to 11 charges including hacking with intent, six counts of blackmail, encouraging hacking, offering to supply data in connection with fraud, and possession of articles for fraud.Kelley made no reaction as he was jailed and his father declined to comment as he left the Old Bailey.Speaking outside court, Detective Constable Rob Burrows, of the Metropolitan Police cyber crime unit, described Kelley as a “prolific and ruthless” hacker. A “cruel and calculating” cyber criminal who took part in a massive TalkTalk hack and blackmailed former chief executive Dido Harding has been locked up for four years.Daniel Kelley, from Llanelli, South Wales, 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 has Asperger’s syndrome and has suffered from depression and extreme weight loss since he 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.Previously, prosecutor Peter Ratliff has described Kelley as a “prolific, skilled and cynical cyber-criminal” who was willing to “bully, intimidate, and then ruin his chosen victims from a perceived position of anonymity and safety – behind the screen of a computer”. He said: “The convictions and sentencing today send out a clear message to cyber criminals committing crime anonymously online – they will be identified and prosecuted for their destructive crimes.” Want the best of The Telegraph direct to your email and WhatsApp? Sign up to our free twice-daily Front Page newsletter and new audio briefings.