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.

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.

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.

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.

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

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

For decades, Berkshire Hathaway (NYSE:BRK-A)(NYSE:BRK-B) has been synonymous with Warren Buffett, the legendary investor whose Midas touch turned a modest textile company into a global powerhouse. However,