Fintech payments company Block (SQ) is down 17% after being the subject of the latest attack from notable short-seller Hindenburg Research.

"Our two-year investigation has concluded that Block has systematically taken advantage of the demographics it claims to be helping," said Hindenburg. "The 'magic' behind Blockrs business has not been disruptive innovation, but rather the companyrs willingness to facilitate fraud against consumers and the government, avoid regulation, dress up predatory loans and fees as revolutionary technology, and mislead investors with inflated metrics."

Block was founded and is led by former Twitter (TWTR) CEO Jack Dorsey. An outspoken proponent of bvitcoin (BTC), Dorsey has led Block into offering bitcoin purchases and the development of a bitcoin wallet and mining rigs.

Bitcoin revenue, however, remain a small part of Block's overall business, which is dominated by the company's Cash App, and which is the focus of the Hindenburg report.

Hindenburg continued: "Our research indicates, however, that Block has wildly overstated its genuine user counts and has understated its customer acquisition costs. Former employees estimated that 40%-75% of accounts they reviewed were fake, involved in fraud, or were additional accounts tied to a single individual."

"We have reviewed the full report in the context of our own data and believe itrs designed to deceive and confuse investors," said Block in a Thursday afternoon response to the report. "We intend to work with the SEC and explore legal action against Hindenburg Research for the factually inaccurate and misleading report they shared about our Cash App business today."

Updated March 23, 17:40 UTC: Includes Block's response.