Minneapolis ? The stock options scandal claimed its biggest corporate chief yet Sunday, with UnitedHealth Group Inc. saying Chairman and CEO William McGuire would step down because an outside report found that his option grants “were likely backdated.”

In one example after another, the report by a firm hired by the company’s board said McGuire’s huge awards of stock options got a boost in value because they were issued on one day but priced as if they’d been issued earlier, when the stock price was lower.

That prompted UnitedHealth’s board to announce sweeping changes Sunday.

UnitedHealth, the nation’s second-largest managed care company, named its president and chief operating officer Stephen Hemsley to be the new CEO. It installed Richard Burke, the founding CEO of UnitedHealth’s predecessor company, as chairman.