Marcus Hutchins was praised in May 2017 for putting an end to the global WannaCry cyber attack.
A British man once hailed a hero for stopping a major global ransomware attack announced on Friday that he has pleaded guilty to US criminal charges for writing malware.
Marcus Hutchins, 24, made the announcement on his website, adding: "I regret these actions and accept full responsibility for my mistakes."
The charges, he said, relate to events "prior to my career in security" and that "having grown up, I've since been using the same skills that I misused several years ago for constructive purposes."
The malware analyst was praised in May 2017 for finding the "kill switch" to the WannaCry cyber attack which impacted multinationals and government services around the world, including Britain's National Health Service.
But he was arrested just three months later as he was returning home from Las Vegas where he had been attending the Def Con Hacking Conference. He was charged with 10 counts of a superseding indictment.
He was wanted for his role, between 2012 and 2015, in creating and selling a malicious computer code known as Kronos targeting banks to steal personal information, including usernames, passwords, email addresses and financial data, court documents show.
The documents reveal that the two counts Hutchins pleaded guilty two both carry prison sentences of up to five years and fines of up to $250,000 (€222,300).