Shares of Super Micro Computer ( SMCI ), or Supermicro, dropped 15% to lead S&P 500 decliners Thursday on a report that the U.S. Department of Justice (DOJ) is investigating the server maker over possible accounting and other violations.

The Wall Street Journal reported that the probe came after well-known short seller Hindenberg Research claimed last month that it saw “fresh evidence of accounting manipulation, sibling self-dealing and sanctions evasion” at Supermicro.

Hindenberg said in the report that it uncovered “glaring accounting red flags, evidence of undisclosed related party transactions , sanctions and export control failures, and customer issues.”

Looking Into Supermicro Whistleblower Accusations

The paper said that the investigation is in its early stages, and that a prosecutor in the U.S. attorney’s office in San Francisco has contacted people who might have relevant information.

It added that officials appear to be looking into accusations from a former employee who filed a whistleblower lawsuit against the company and Chief Executive Officer (CEO) Charles Liang in April, charging Supermicro with improper accounting .

Last month, Supermicro announced that it would delay the release of its annual report, saying that management needed additional time “to complete its assessment of the design and operating effectiveness of its internal controls over financial reporting as of June 30, 2024.”

Supermicro didn’t respond to an Investopedia request for comment.

Super Micro Computer shares hit an all-time high in March , quadrupling in value for the year at that point as the company benefited from the artificial intelligence (AI) boom. However, the stock has lost ground since, although it remains up about 38% in 2024. Recently, shares were off 15% at $387.21 each.