The health insurance giant has called a new report from WSJ “misinformation,” but investors may not be so sure. Shares were down about 9% early Friday. UnitedHealth Group, America’s largest insurer, is facing yet another crisis.

UnitedHealth Group stock fell sharply Friday following a report that said the Justice Department had launched a civil fraud investigation into the company’s Medicare billing practices.The DOJ probe aims to examine the healthcare company’s practices for documenting diagnoses that trigger extra payments to its Medicare Advantage plans,

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