It is believed the British computer expert was detained after a trip to Las Vegas.
WannaCry attack hero Marcus Hutchins arrested in US
A computer expert, who was credited with stopping a cyber attack on Britain’s National Health Service, has been arrested in the United States.
Marcus Hutchins, a 23-year-old researcher from Britain, was reportedly detained by the FBI in Nevada after a trip to Las Vegas.
Mr Hutchins helped to foil the WannaCry ransomware attack, which targeted 300,000 computers in 150 countries in May.
The US Department of Justice said he had been arrested for alleged involvement in a separate incident between 2014 and 2015.
"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," it said.
"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."
Andrew Mabbitt, founder of a cyber security company and friend of the IT expert, reported that Mr Hutchins, also known as Malware Tech, had been arrested on Wednesday.
Mr Mabbitt tweeted on Thursday: “I can confirm @MalwareTechBlog was detained yesterday and FBI/US Marshalls won't tell me where he is.”
In a tweet an hour later, he said that Mr Hutchins was being held at the Las Vegas FBI field office and appealed for help with securing legal representation.
“Finally located @MalwareTechBlog, he's in the Las Vegas FBI field office. Can anyone provide legal representation?” Mr Mabbitt added.
The UK’s National Cyber Security Centre confirmed that a British citizen had been arrested but declined to comment any further.
"We are aware of the situation," a spokesman said. "This is a law enforcement matter and it would be inappropriate to comment further."