Marcus Hutchins appeared in a Wisconsin court on Thursday after he agreed last month to plead guilty to developing a malware called Kronos and conspiring to distribute it from 2012 to 2015.
Prosecutors dismissed eight more charges in exchange for his plea.
Sentencing for Hutchins is set for July 26. He faces up to 10 years in prison but could receive a more lenient sentence for accepting responsibility.
Hutchins’s arrest in Las Vegas in August 2017 came as a shock because months earlier he was hailed as a hero for finding a “kill switch” to the WannaCry virus that crippled computers worldwide.