Giant French contractor VINCI Group is investigating a hoax release of damaging, false financial information that, on Nov. 22, led to trading in the firm's shares being suspended on the Euronext Paris exchange.

France’s financial regulator, AMF, describes the event as a “serious market dysfunction” and is looking into whom it might have benefitted.

According to VINCI, the Bloomberg and Dow Jones news agencies reported allegations of accounting irregularities in the firm's 2015 financial year, resulting in the dismissal of its chief financial officer.

Minutes after checking with VINCI, the news agencies published corrections, but the company's shares tumbled 18%. VINCI denied all the claims. According to the contractor, the hoaxers created a false VINCI website and, on Nov. 22 between 4:05 p.m. and 5:35 p.m., released three malicious, downloadable press releases.

Share values bounced back once trading resumed.