The U.S. Department of Justice has reportedly launched an investigation into UnitedHealth Group's (NYSE: UNH) Medicare billing practices. Investors were shaken by the report, sending UnitedHealth shares down 9% as of 10 a.

The stock is having its worst day in five years, even as the company denied any new Justice Department investigation and a Mizuho analyst recommended buying.

Key Takeaways U.S. equities dropped at midday following the latest data on consumer sentiment and a report that UnitedHealth Group is under a federal probe. UnitedHealth Group is said to be facing a Department of Justice probe of its Medicare billing practices.