• ProPublica reported Thursday that Warren Buffett may have violated Berkshire Hathaway's ethics policies.

• Leaked IRS data seen by ProPublica showed that Buffett sold shares in stocks that Berkshire was trading.

• Buffett has previously said that trading the same stocks as Berkshire would pose a conflict of interest.

Legendary investor Warren Buffett may have violated Berkshire Hathaway's ethics policies — which he himself wrote — by personally trading the same stocks as the conglomerate, according to a ProPublica report on Thursday.

While changes in Berkshire's stock portfolio are closely watched by investors, Buffett has largely been quiet about his personal holdings.

But leaked IRS data obtained by ProPublica show that in the last two decades he made trades in his personal portfolio on the same companies that Berkshire bought or sold during the same quarter or the quarter before.

The company did not immediately respond to Insider's request for comment. Buffett also didn't respond to ProPublica's request for comment.

Berkshire's ethics policies say "all actual and anticipated securities transactions of Berkshire" have to be publicly disclosed before company employees can personally trade those stocks.

And Buffett himself has said previously that he "can't be buying what Berkshire is buying," and that doing so would present a conflict of interest.

Yet ProPublica reported that Buffett made at least $466 million in personal stock sales between 2000 and 2019, though the records it viewed didn't include securities he bought and held.

Here are the three stock sales ProPublica uncovered:

On April 24, 2009, Buffett sold $20 million worth of Wells Fargo shares in his personal account. ProPublica didn't specify a particular transaction Berkshire made in the stock but noted the company was already a large shareholder.

In August 2009, Buffett personally sold $25 million in Walmart stock. It's not clear which came first, but that same quarter, Berkshire roughly doubled its stake in the retailer.

In October 2012, Buffett privately sold $35 million of Johnson & Johnson shares, which Berkshire also sold. A filing at the end of the quarter did not specify a date. The conglomerate later sold millions more shares in the subsequent two quarters.

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