Marcus Hutchins, a 22-year-old British computer expert who helped stop the WannaCry ransomware attack in May, has been arrested after attending the Def Con hacking conference here, local media reported Thursday.

The young cyber security expert was detained Wednesday by the FBI for allegedly helping create and distribute the Kronos banking trojan between July 2014 and July 2015, according to the website MotherBoard, which first reported the story.

Hutchins, known as MalwareTech on Twitter, is quite active online, but since Wednesday, no tweet has been posted on his account @MalwareTechBlog.

"I can confirm @MalwareTechBlog was detained yesterday and FBI/US Marshalls won't tell me where he is," Andrew Mabbitt, a cyber security company founder and Hutchins' friend, tweeted on Thursday, saying that he does not believe the charges against Hutchins.

"He spent his career stopping malware, not writing it," tweeted Mabbitt.

The Kronos malware, which is spread through malicious email attachments, can be used to steal banking passwords and other credentials from infected computers.

Hutchins was hailed a hero in May for discovering a "kill switch" for the WannaCry ransomware to delay its global spreading as it infected and forced hospitals, telecom providers and many other businesses worldwide to shut down.

The WannaCry ransomware encrypted files of hundreds of thousands of computers and then charged victims Bitcoins worth 300 to 600 U.S. dollars as ransom.

In total, the hackers made about 140,000 dollars in Bitcoin from the attack, which had been steadily deposited in three anonymous online wallets.

But on Wednesday night, right after Hutchins' detention, the hackers behind the global WannaCry ransomware attack abruptly cashed out all their ransom payments within fifteen minutes, though there is no indication that the two events are connected.