The reported probe adds to a string of recent setbacks that have erased more than half, or over $300 billion, from its market value since November.

The Justice Department is investigating UnitedHealth Group for possible criminal Medicare fraud, people familiar with the matter said. The healthcare-fraud unit of the Justice Department’s criminal division is overseeing the investigation,

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. UnitedHealth said it had not been notified by the DOJ about the "supposed criminal investigation reported,