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 rebounded modestly Wednesday following yesterday's crash, with analysts from UBS, Oppenheimer, and Morgan Stanley leaving their ratings unchanged after the health insurer pulled its outlook and announced its CEO had stepped down.

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.

UnitedHealth Group is being investigated for possible Medicare fraud, according to The Wall Street Journal, sending shares of the healthcare company sliding in after-hours trading just one day after its CEO,