Block Inc co-founder Jack Dorsey’s net worth has been hit hard after a new report from Hindenburg Research said the payments company ignored widespread fraud.

Dorsey’s fortune plummeted $526 million on Thursday. His biggest one-day drop since May. According to the Bloomberg Billionaires Index, his now worth $4.4 billion after falling 11%.

The stock fell 65% to 75% “on a purely fundamental basis” after Hindenburg released a report on Thursday claiming that Block had inflated user metrics. The company denied the allegations and plans to take legal action against the short sellers.

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

Dorsey, also the co-founder of Twitter, has most of his personal wealth tied to Block. The Bloomberg Wealth Index estimates his stake in the company is worth $3 billion, while his stake in Elon Musk’s social media company is worth $388 million.

It is not the first time Hindenburg, run by Nathan Anderson, has singled out billionaires and let their fortunes slide.

Earlier this year, the firm released an investigation into India’s Gautam Adani and his empire, sending his company’s stock plummeting and wiping tens of billions of dollars from his net worth.

Once the world’s second-richest person, Adani ranks 21st on the Bloomberg Wealth Index with a fortune of $60.1 billion.

In September 2020, Hindenburg also targeted electric car maker Nikola Corp. Nikola’s shares have since plummeted. An investigation led to the indictment of its founder, Trevor Milton, on fraud charges in October.