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,

The U.S. Department of Justice is carrying out a criminal investigation into UnitedHealth Group for possible Medicare fraud, the Wall Street Journal reported on Wednesday.

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.