Our 2-year investigation has concluded that Block has systematically taken advantage of the demographics it claims to be helping,” Hidenburg Research said in a note published on its website. Hindenburg Research said on Thursday it held short positions in Block Inc, alleging that the Jack Dorsey-led payments firm overstated its user counts and understated its customer acquisition costs. Shares of Block fell 18% in premarket trading after the report. Block did not immediately respond to a Reuters request for comment. The U.S. short-seller, behind a market rout of over $100 billion in India’s Adani Group, said in its latest report that former Block employees estimated that 40%-75% of accounts they reviewed were fake, involved in fraud, or were additional accounts tied to a single individual. (ALSO READ: Why Hindenburg Research decided to short only Adani stocks listed outside India Reuters could not verify the claims raised by Hindenburg against Block. About 5.2% of Block’s free float shares were in short position as of March 22, according to Ortex data. Founded in 2017 by Nathan Anderson, Hindenburg Research is a forensic financial research firm that analyses equity, credit and derivatives. It has a track-record of finding corporate wrongdoings and placing bets against the companies.