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Warren Buffett's Berkshire Hathaway built a $1.6 billion stake in UnitedHealth last quarter, marking one of its last wagers with the investor as CEO.

The investment comes as UnitedHealth faces soaring medical costs, federal investigations, the fallout of the killing of a top executive and a cyberattack last year.

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Berkshire Hathaway recently filed its second-quarter 13F form, revealing its stock holdings at the end of June.

Warren Buffett is known for seeking out stocks of companies that possess wide economic moats — businesses with durable competitive advantages that fend off rivals and ensure long-term profitability. These moats,

UNH stock soared after Warren Buffett’s Berkshire Hathaway revealed it bought shares of the healthcare company. Nonetheless, UnitedHealth faces a long list of unresolved issues.

Leveraged positions in the stock market jumped 18% in one month and topped $1 trillion for the first time. Increasing use of debt to invest can tell us a lot about investors' attitudes. And while this has always been the case,