UnitedHealth under investigation over alleged Medicare fraud, report says - UnitedHealth said it was not notified about the “supposed criminal investigation reported.”

Stephen Hemsley ran UnitedHealth Group for more than a decade. It's a different company after four years with Andrew Witty in charge.

UnitedHealth Group shares fell nearly 6% in premarket trading on Thursday, after the Wall Street Journal reported that the U.S. Department of Justice was investigating the company for potential Medicare fraud.

Former CEO and current chairman Stephen Hemsley is stepping back into the top job following the abrupt resignation of Andrew Witty, UnitedHealth said.

UnitedHealth's stock has plunged nearly 40% year-to-date as the company has battled a series of crises. Can the healthcare giant turn it around? Seeking Alpha analysts weigh in.

UnitedHealth Group, the largest health insurer in the country, is turning back the clock in a moment of crisis. On Tuesday, the company announced that chairman Stephen Hemsley is returning as CEO, stepping back into the role he left in 2017.