A British cyber security expert credited with stopping the ransomware attack on the NHS today pleaded not guilty to US charges that he creating malicious software to steal banking information.

Marcus Hutchins - who entered the plea at a court in Milwaukee, Wisconsin - and a co-defendant face charges of conspiring to commit computer fraud in the state and elsewhere in 2014. 

The 23-year-old was arrested on August 2 at Las Vegas Airport on his way home to Ilfracombe in Devon after a cyber security convention in the US. 

Hutchins, also known as MalwareTech, was hailed a hero in May this year when he found a 'kill-switch' that slowed the effects of the WannaCry 'ransomware' virus that crippled the NHS and hit more than 300,000 computers in 150 countries. 

But the charges relate to alleged conduct occurring between July 2014 and July 2015, long before he found a way to stop the WannaCry ransomware virus.

In his first public comments since his arrest, Hutchens revealed that he will be able to go online once more and that he plans to write a blog as a result of relaxed bail conditions.

On his Twitter account he wrote: 'There's a lot of people I'd like to thank for amazing support over the past 11 days, which I will do when I get a chance to publish my blog.

'I'm still on trial, still not allowed to go home, still on house arrest; but now I am allowed online. Will get my computers back soon. The list included partying, renting supercars, visiting Red Rock Canyon - and being 'indicted by the FBI'. 

Prosecutors allege that before Hutchins won acclaim he created and distributed a malicious software called Kronos to steal banking passwords from unsuspecting computer users. 

In addition to computer fraud, the indictment lists five other charges, including attempting to intercept electronic communications and trying to access a computer without authorisation.

The indictment says the crimes happened between July 2014 and July 2015, but the court document doesn't offer any details about the number of victims. 

Prosecutors have not said why the case was filed in Wisconsin. The name of Hutchins's co-defendant is redacted from the indictment.

Hutchins has been granted computer access for work while his case is pending. It was not clear from today's brief hearing what that work would entail.