(Bloomberg) -- Block Inc. co-founder Jack Dorsey’s net worth was hammered after Hindenburg Research’s latest report, which alleged the payments company ignored widespread fraud.

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Dorsey’s fortune plunged by $526 million on Thursday, his worst single-day decline since May. He’s now worth $4.4 billion after the 11% drop, according to the Bloomberg Billionaires Index.

Hindenburg released a report Thursday claiming Block had inflated user metrics, and that the stock has downside of 65% to 75% “on a purely fundamental basis.” The company denied the allegations and said it plans to explore legal action against the short-seller.

Block fell as much as 22% on Thursday, before closing down 15%.

Dorsey, who also co-founded Twitter, has most of his personal fortune tied up in Block. The Bloomberg wealth index estimates his stake in the firm is worth $3 billion, while his position in Elon Musk’s social media company is valued at $388 million.

It’s not the first time that Hindenburg, run by Nathan Anderson, has singled out billionaires and sent their fortunes falling.

The firm released an investigation into India’s Gautam Adani and his empire earlier this year, causing his companies’ stocks to plummet and erasing tens of billions of dollars from his net worth.

Adani, who at one point was the world’s second-richest person, now ranks 21st on Bloomberg’s wealth index with a $60.1 billion fortune.

Hindenburg also targeted electric carmaker Nikola Corp. in September 2020. Nikola’s stock plunged in the aftermath and an investigation led to a fraud conviction against its founder Trevor Milton in October.

--With assistance from Jack Witzig.

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