A Bronx man allegedly received $1.5 million in just ten months. A California real estate broker raked in more than $500,000 within half a year. A Nigerian government official is accused of pocketing over $350,000 in less than six weeks.

What they all had in common, according to federal prosecutors, was participation in what may turn out to be the biggest fraud wave in U.S. history: filing bogus claims for unemployment insurance benefits during the COVID-19 pandemic. (The broker has pleaded guilty, while the Bronx man and Nigerian official have pleaded not guilty.)

One person, according to the U.S. Department of Labor, used a single Social Security number to file unemployment insurance claims in 40 states. Twenty-nine states paid up, sending $222,532.

But the problem extends far beyond a plague of solo scammers. Bots filing bogus applications in bulk, teams of fraudsters in foreign countries making phony claims, online forums peddling how-to advice on identity theft – all inside the infrastructure of perhaps the largest fraud wave in history.

A ProPublica investigation reveals that much of the fraud has been organized – both in the U.S. and abroad. Fraudsters have used bots to file online claims in bulk. And others, located as far away as China and West Africa, have organized low-wage teams to file phony claims.

The fraud has been enabled by a burgeoning online infrastructure, whose existence has not previously been reported in the mainstream press. Much of it is geared toward exploiting aging or obsolete state unemployment systems whose weaknesses have drawn warnings for decades.

Communities have sprouted on messaging apps such as Telegram, where fraudsters trade tips on how to cash in. Hustlers advertise their techniques – or “sauces” (apparently short for “secret sauce”) – for filing bogus claims, along with state-specific instructions on how to get around security checks, according to a ProPublica review of messages on more than 25 such chat forums.

Some of the forums have thousands of participants and regularly offer stolen identities for sale, alongside tech tips, screenshots that ostensibly prove the methods work and advice on which states are easiest to game and which are “lit” – that is, still paying out fake claims. Users have created two Telegram channels in which they trade tips for filing claims in Maryland, whose labor department recently said it detected some 508,000 potentially fraudulent jobless claims between the start of May and mid-June. Participants in those forums have been talking about turning their efforts to Pennsylvania, where officials recently said they have “noticed an uptick” in fraudulent claims.

“From my experience, when this is all said and done, we are going to be counting in the hundreds of billions of dollars, not the tens of billions,” said Jon Coss, who heads a unit within Thomson Reuters that is helping states detect fake unemployment insurance claims.

Coss bases that assessment on the widespread fraudulent activity he’s seen. He said one U.S. state, which he declined to name, received fake claims – all purportedly from state residents – that originated from IP addresses in nearly 170 countries. They included countries historically linked to fraud, such as China, Nigeria and Russia, as well as more surprising ones, such as Cuba, Eritrea, Fiji and Monaco.

Overall, Coss said, between 40% and 50% of the claims his group has analyzed seem highly suspect. He added, “It’s mind-boggling the level of fraud that we’re seeing.”