In a filing with the Securities and Exchange Commission, United Health Group said it has "full confidence" in its practices. It added that a court-appointed monitor found no wrongdoing after a decade-long probe into its Medicare Advantage business.

UnitedHealth shares tumbled Thursday after the health insurance giant confirmed that it’s the subject of a Department of Justice investigation. Monitor these key chart levels.

UnitedHealth Group confirmed Thursday that the U.S. Department of Justice is investigating how it bills for its Medicare Advantage plans.

UnitedHealth Group confirmed Thursday that its Medicare program is under investigation by the US Department of Justice and that it is working with the agency.

Justice Department launched probe into UnitedHealth's Medicare billing practices as the insurance company experiences leadership shifts, company says.

UnitedHealth Group has said it is under investigation by the Department of Justice, which is probing its involvement in Medicare, a federal health insurance program for those over 65 and people with disabilities. Newsweek reached out to the Department of Justice for comment.

Stocks were mixed Thursday and the Dow Jones Industrial Average declined following slumps in Honeywell and IBM after the companies issued quarterly earnings updates and as UnitedHealth Group traded lower after saying it was “complying with formal criminal and civil requests” from the U.S. Department of Justice.