NEW YORK (AP) — Authorities in New York City said Thursday they disrupted an online fraud operation that stole millions of dollars by duping victims into making phony cryptocurrency investments.

Brooklyn District Attorney Eric Gonzalez said his office seized 21 web domains that were being used by scammers in so-called “pig butchering” schemes, a term that refers to gaining victims’ trust through dating apps or other sites and steering them toward bogus investments.

“Pig butchering is a growing type of scam that defrauds residents of Brooklyn and the entire country out of billions of dollars every year,” Gonzalez said in a statement. “My office’s strategy is to disrupt these schemes by seizing and shutting down their online infrastructure, and to educate the public.”

He urged people not to trust crypto investments that seem too good to be true and warned against downloading apps from unverified crypto websites.

The New York Police Department received 50 complaints about online crypto scams last year, but that is likely a tremendous undercount because people are ashamed of being fooled or don’t know how to report the crime, Gonzalez said.

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The victims who have come forward reported losing more than $4 million in Brooklyn alone, Gonzalez said, calling the reports “heartbreaking.”

“There are people who are losing huge sums of money,” he said during a news conference. “Sometimes they’re losing their entire life savings. Sometimes they’re mortgaging their homes.”

One victim, a 51-year-old woman, reported to police last year that she lost $22,680 after she was added to online chat groups discussing crypto investments.

The woman made eight deposits and saw statements showing her account grew to $387,495. But, when she tried to withdraw her initial investment, she was told she had to pay taxes. She complained, and she was blocked from the chat group. Her money was gone, Gonzalez said.

Investigators learned that the woman’s money was moved through multiple cryptocurrency addresses, deposited into an account at a foreign crypto exchange and cashed out by an individual in a region beyond U.S. jurisdiction, possibly China. The investigation found additional victims of the same scheme from California, Pennsylvania, and Illinois who had lost a total of $366,665, Gonzalez said.

Another woman who spoke anonymously in a video shared by the district attorney’s office said a scammer first reached her through a dating app.

“His flirting made me feel secure and trusting,” said the woman, who was trying to buy her former husband out of their house.

Though she said she hesitated when the scammer first told her to invest in crypto, she ultimately lost $118,000 after tapping a personal loan and her pension.

“I feel like an idiot,” she said.