Shares of UnitedHealth Group slumped 6% in premarket trading Thursday on a report that the U.S. Department of Justice is investigating the embattled health insurance provider for possible criminal Medicare fraud.

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 stock has plummeted since my last Buy rating and is ~55% off highs, but its lower valuation now offers a significant margin of

May 13 (UPI) -- UnitedHealth Group announced Tuesday CEO Andrew Witty will step down, citing "personal reasons." Witty will leave the role of CEO and be replaced by Stephen J. Hemsley, effective immediately.

Former UnitedHealth Group chief executive officer Stephen Hemsley to replace Andrew Witty. Here's what we know.

UnitedHealth Group CEO Stephen Hemsley, who replaced Andrew Witty, said he has the right strategy in place “for the era ahead.”