A judge in the US state of Nevada has recommended the release on $30,000 (£23,000) bail of a UK computer expert.
Prosecutors told the court that Marcus Hutchins had admitted to writing and selling malware code designed to steal banking details.
His lawyer said he denied all the charges against him.
Mr Hutchins 23, from Ilfracombe in Devon, came to prominence after he stalled the WannaCry cyber-attack that hit the NHS in May.
Federal judge Nancy Kobbe ordered Mr Hutchins’ release on bail pending his next appearance in Wisconsin on 8 August subject to a lengthy list of conditions including the surrender of his passport and monitoring by GPS.
However, Mr Hutchins will have to spend the weekend in jail after failing to post $30,000 bail before the court closed on Friday.
As he left the courtroom Mr Hutchins was ordered to walk with his hands behind his back but he was not shackled.
No members of his family were present in court but defence lawyer Adrian Lobo presented the judge with a bundle of letters.
She said they were from friends and relatives showing support for a client who had never been in trouble with the law in the US or the UK.
Ms Lobo told the BBC: “He’s pled not guilty. He is standing by that and he fights the charges and we intend to fight the case in Wisconsin.”
She described the federal indictment against him as “pretty flimsy, it’s pretty slim compared to what we normally see in a United States indictment.”
Earlier in court government lawyer Dan Cowhig said Mr Hutchins had admitted in an interview that he wrote the code for a malware programme known as Kronos and indicated that he had sold the code.
Mr Cowhig said the US government had evidence of internet chat room logs in which the defendant allegedly discussed splitting the proceeds of the sale with an associate and later complained about the amount he had received.
At the scene
By James Cook, BBC North America correspondent
There was no missing Marcus Hutchins as he was brought into courtroom 3C of the US District Court in Las Vegas.
The “surfer who saved the world” was wearing a bright yellow custody-issue T-shirt and trousers along with luminous orange socks and sandals.
Judge Nancy Kobbe was sympathetic to the defendant’s plea to be released on bail, waving away a claim from a government lawyer that the cyber-security expert posed a risk to the public because he had gone shooting on a gun range popular with tourists.
Mr Hutchins was so softly spoken that several times Ms Kobbe had to ask him to raise his voice.
Mr Hutchins was arrested at Las Vegas airport minutes before he was due to fly home from a week of partying in the desert city
He had been attending a cyber-security conference.
Among his fellow computer experts he is regarded as a hero for his role in stopping the so-called WannaCry virus that hit the NHS before spreading to 150 countries.
Mr Hutchins has been accused of involvement with Kronos – a piece of malware used to steal banking logins from victims’ computers.
The FBI arrested him on Wednesday.
WannaCry spread rapidly through computer systems around the world, in an unprecedented outbreak that began on 12 May.
Shortly afterwards, Mr Hutchins was thrust into the limelight after he found a way to stop it from spreading.
He had been in Las Vegas attending the Black Hat and Def Con cyber-security conferences but activity on his Twitter feed – usually highly active – ceased two days ago.
The US Department of Justice (DoJ) said in a statement: “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.”
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