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.

UnitedHealth Group shares tumbled early Friday on a report that the U.S. Department of Justice has started an investigation into the health care giant’s Medicare billing practices.

The Justice Department is investigating UnitedHealth's Medicare billing practices, focusing on diagnoses that led to higher federal payments. The probe follows reports that the company received billions for questionable diagnoses in its Medicare Advantage plans.