Medicare practices sent the stock diving Thursday to a five-year low. The Justice Department is looking into potential Medicare fraud by the health insurer, according to a report by the Wall Street Journal,

Shares of UnitedHealth Group tumbled more than 15% in morning trade on Thursday after a report said that the Justice Department is investigating the health insurer for potential fraud.

UnitedHealth Group shares plunged nearly 13% today after a Wall Street Journal report that the U.S. Department of Justice had begun a criminal investigation into the company for potential Medicare fraud.