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

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.

Today, we're looking at Warren Buffett's Berkshire Hathaway's (BRK-B) decision to sell Apple (AAPL) shares while adding UnitedHealth Group (UNH) shares. Editor's note: This post was updated to reflect the proper name for UnitedHealth Group.

Berkshire Hathaway just disclosed that it dumped $1.6 billion into a sinking ship, and Wall Street instantly paid attention.