A British computer whizz who helped stop a world-wide cyber-attack has been arrested in the US on suspicion of being involved in creating software that harvested banking details.

Marcus Hutchins, the Devon-born tech expert also known as MalwareTech, helped foil the WannaCry “ransomware” virus that hit more than 300,000 computers.

The NHS was one of the many organisations across 150 countries struck by the virus in May, before Hutchins, 23, discovered a ‘kill-switch’ that stopped it.

According to US authorities, he was arrested at Las Vegas’s McCarran International Airport on Wednesday and was charged with creating banking malware.

The US Department of Justice said the allegations do not relate to the worldwide cyber-attack.

It said: “Marcus Hutchins… a citizen and resident of the United Kingdom, was arrested in the United States on 2 August, 2017, in Las Vegas, Nevada, after a grand jury in the Eastern District of Wisconsin returned a six-count indictment against Hutchins for his role in creating and distributing the Kronos banking Trojan.

“The charges against Hutchins, and for which he was arrested, relate to alleged conduct that occurred between in or around July 2014 and July 2015.”

According to Motherboard, Hutchins was arrested while at the airport after attending a hacking conference.

The indictment includes allegations that he created, advertised and sold banking malware on the darkweb.

The malware is used to direct users to fake websites where they would then enter their banking details.

The cyber community expressed their concern over his arrest with Naomi Colvin, from civil liberties campaign group Courage, praising him for his earlier work.

She said: “In May this year, WannaCry malware closed hospitals in the UK, becoming the first ransomware attack to represent an actual threat to life.

“In halting the spread of WannaCry before the US woke up, MalwareTech did the world an enormous service – and to American businesses in particular.”

Ms Colvin said he had been detained for 24 hours before information was released about his arrest and said he has still not been allowed to contact his family or lawyers.

“The US treats hackers far worse than other countries do, with much longer prison sentences, a dearth of vital health care and rampant solitary confinement,” she said.

And Hutchins’ mother, Janet Hutchins, said it was “hugely unlikely” that her son was involved because he has spent “enormous amounts of time and even his free time” combating such attacks.

She added that she is “outraged” by the charges and has been “frantically calling America” trying to contact her son.