A 35-year-old Chinese man has been tagged as the alleged mastermind behind a gargantuan botnet used to steal billions from zombie computers

The U.S. Department of Justice quoted FBI Director Christopher Wray as saying Wednesday that the “911 S5” botnet — a network of malware-infected computers in nearly 200 countries — was likely the world’s largest.

Justice said in a news release that Yunhe Wang, 35, was arrested May 24. Details about where he was detained were not available and a department spokesperson said “we are not commenting beyond our press release.”

The cybercriminals used a network of zombie residential computers to steal “billions of dollars from financial institutions, credit card issuers and accountholders, and federal lending programs since 2014,” according to an indictment filed in Texas’ eastern district.

The administrator, Wang, sold access to the 19 million Windows computers he hijacked — more than 613,000 in the United States — to criminals who “used that access to commit a staggering array of crimes that victimized children, threatened people’s safety and defrauded financial institutions and federal lending programs,” U.S. Attorney General Merrick Garland said in announcing the takedown.

He said criminals who purchased access to the zombie network from Wang were responsible for more than $5.9 billion in estimated losses due to fraud against relief programs. Officials estimated 560,000 fraudulent unemployment insurance claims originated from compromised IP addresses.

Wang allegedly managed the botnet through 150 dedicated servers, half of them leased from U.S.-based online service providers.

The indictment says Wang used his illicit gains to purchase 21 properties in the United States, China, Singapore, Thailand, the United Arab Emirates and St. Kitts and Nevis, where it said he obtained citizenship through investment.

In its press release, the Justice Department thanked police and other authorities in Singapore and Thailand for their assistance.