Warren Buffett's Berkshire Hathaway's recent purchase of $1.57 billion worth of UnitedHealth Group shares has sent the company's stock soaring in premarket trading. This significant investment comes as UnitedHealth faces several challenges, including federal investigations into its Medicare Advantage business and recent financial setbacks. Despite the positive market reaction, UnitedHealth's stock has still lost roughly half its value over the past year due to rising healthcare costs and other difficulties.

Prepared by Christopher Adams and reviewed by editorial team.