A young hacker who caused global chaos and "incalculable" damage by fuelling more than 1.7 million cyber attacks around the world will be sentenced tomorrow.

Adam Mudd, 20, helped fellow hackers to attack and crash websites and computer servers by selling access to his sophisticated TitaniumStresser programme.

The court heard Mudd's distributed denial of service (DDoS) programme, designed in his bedroom in Hertfordshire when he was just 15-years-old, crippled computers in "every major city" around the world, causing millions of pounds of damage.

He first road-tested the programme on the website of West Herts College, where he himself was studying computer science, causing "incalculable" harm.

Prosecutor Jonathan Polnay told the court TitaniumStresser users, paying up to £250 to subscribe, could target websites, email systems, and file transfer services, as well as online gamers using XBox Live, PlayStation, RuneScape and Minecraft.

TitaniumStresser would "overwhelmed" the servers of the victim with an avalanche of online requests sent simultaneously, and gave users the option of logging a list of their "friends and enemies".

Mr Polnay showed the court a map of the world showing attacks in "almost every major city", adding: "Where there are computers, there have been attacks."

He said it would be "impossible" to assess the financial damage done by Mudd's systems, but said one of Mudd's four attacks on West Herts College in 2014 "was so large it is likely to have affected a further 70 schools and higher education establishments, including the Universities of Cambridge, Essex and East Anglia as well as local and district councils."

Mudd, who lives in Toms Lane, Kings Langley, raked in more than £250,000 through subscriptions to TitaniumStresser - in bitcoins and US dollars - before reaching his 18th birthday.

“Titanium Stresser is a computer programme created by the defendant, and it is not an unimpressive piece of software in terms of design”, said Mr Polnay.

“It carried out DDoS attacks and it takes down computer networks and websites.

“The defendant charged for use of it, to others all around the world – these offences truly had a global reach – would pay money to use this programme.”

He said the TitaniumStresser internal log showed it had been used for 1,738,828 cyber attacks between September 2013 and March 2015.

Mr Polnay added that Mudd appears to have saved the most powerful attack capabilities of his programme for himself, using it nearly 600 times on 181 victims under the username themuddfamily.

More than 666,000 computers were targeted by Mudd's programme, including 52,836 in the UK, before he was finally snared by police.

Mudd opened his computer for officers when he was arrested in March 2015, admitting he had made TitaniumStresser but claiming "he had not been involved in any criminality".

However he pleaded guilty to doing unauthorised acts with intent to impair the operation of a computer, a charge of making, supplying or offering to supply the TitaniumStresser programme, and concealing criminal property in October last year.

Judge Michael Topolski QC said the teenager, who has been assessed for autism, will not be sentenced until a later date.

The court has heard his software code was copied by notorious hackers the Lizard Squad, who claims to have successfully overloaded victims including Microsoft, Sony, and Instagram.

Mudd pleaded guilty to all three charges against him