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.

Buffett & Co. picked up UnitedHealth stock on the cheap, with the embattled blue chip one of the newest holdings in the Berkshire Hathaway equity portfolio.

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

Shares of UnitedHealth Group Inc. (NYSE: UNH) climbed 2.81% in Monday's pre-market trading session, extending Friday's gain following Michael Burry and Warren Buffett's stake acquisition in the insurance behemoth.

B stake in UnitedHealth Group Incorporated signals a market shift. Click for why I have now upgraded UNH stock to Buy.

The company may be under criminal investigation for alleged irregularities in its Medicare business—but it's been touched by the Warren Buffett effect.

Warren Buffett's Berkshire Hathaway has acquired 5 million shares in UnitedHealth Group , a regulatory filing showed on Thursday, sending the health insurer's stock up 7% in extended trading.

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