Berkshire Hathaway’s portfolio added six new stocks, including the three new secret stocks. Warren Buffett was a net seller of stocks for the eleventh straight quarter.

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.

The conglomerate sold Apple shares during the second quarter, though the iPhone maker remains Berkshire’s largest stockholding.

See Berkshire Hathaway Inc.'s strategy with a big new stake in UnitedHealth. Learn how it's hedging against recession and stagflation. Click for my BRK.A update.

I told MarketWatch readers on Aug. 14 that Warren Buffett was about to reveal one big mystery elephant for Berkshire Hathaway’s portfolio — one $5 billion investment in the shares of an industrial giant.

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.

Warren Buffett is the world’s most famous investor and is renowned for his sober, long-term approach to the substantial equity stakes he takes in companies. One of his best-known sayings about Berkshire Hathaway is,

Given Buffett's concern over the stock market, it makes sense for investors to buy the most conservative stocks in the Berkshire Hathaway portfolio.