Block co-founder Jack Dorsey saw his net worth plunge by $526 Thursday after Hindenburg Research accused the payments company of inflating user metrics, Bloomberg reports.

Dorsey is now worth $4.4 billion after the 11% haircut, according to the Bloomberg Billionaires Index.

Hindenburg issued a report Thursday saying that Block (SQ) had a downside of 65% to 75% “on a purely fundamental basis.”

Hindenburg said its information on the inflated number of CashApp users was based on “dozens of interviews with former employees, partners, and industry experts, extensive review of regulatory and litigation records” and public records obtains through the Freedom of Information Act.

Block denied the accusation and announced plans to work with the Securities and Exchange Commission to sue the short seller.

At one point Thursday, Block declined 22%, closing down 15%. Mid-morning Friday, the stock had ticked downwards by 3.43% at $59.76.

Bloomberg estimates as much as $3 billion of Dorsey’s wealth is tied up in Block, and another $388 million in Twitter.