This investment signifies Buffett's re-entry into UNH after liquidating his entire position back in 2010, indicating that he perceives significant value at

UnitedHealth Group (UNH) stock is still down 40% YTD but has surged more than +20% this month following reports that Warren Buffett, and other billionaire hedge fund managers have taken a stake in the company.

The company may be under criminal investigation for alleged irregularities in its Medicare business—but it’s been touched by the Warren Buffett effect. Shares in the troubled private health insurer UnitedHealth Group (NYSE: UNH) are currently seeing their best trading day in months.