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

In May, a 13F filing revealed that Berkshire Hathaway was buying mystery stocks. Now, at last, we know what they are.

Warren Buffett has requested confidentiality in a new Berkshire Hathaway position. Will investors find out the stock Thursday?

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,

Warren Buffett secret stock purchase has been kept confidential for months to avoid triggering copycat trades.

Buffett owned UnitedHealth shares before selling his stake in 2010, though his Berkshire Hathaway recently acquired shares.

Warren Buffett is telling investors something -- not through what he has said, but through his actions with the balance sheet of his investment conglomerate Berkshire Hathaway ( BRK.A -0.40%) ( BRK.B 0.83%). These actions should be taken as a warning sign with the stock market reaching elevated valuation levels in recent months.