Marcus Hutchins, a hacker who helped stop the WannaCry ransomware in May, is in US custody after being arrested in Las Vegas.
The UK security researcher, was detained after leaving the Defcon security conference, ZDNet reported on Thursday, citing multiple friends. It's not clear why he was arrested.
The FBI didn't immediately respond to a request for comment.
The malicious WannaCray software spread to more than 200,000 computers in 150 countries, locking up machines' data unless victims agreed to pay attackers. Hutchins, aka @malwaretechblog, helped thwart the attack by finding a kill switch in the software.