A “cruel and calculating” cyber criminal who took part in a massive TalkTalk hack attack 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.