Many investors follow the moves of billionaires and hedge fund managers very closely, and why not? After all, these are people who have had tremendous success with their investments, so it would seem like a great place to look for ideas and general "smart money" trends.

While it's never a good idea to buy or sell a stock just because a billionaire or hedge fund manager is, it's certainly a great way to find stocks to put on your radar. With that in mind, here are the 10 stocks billionaires and hedge fund managers bought the most of during the fourth quarter of 2017, and the 10 most-sold stocks by the same group in the same time frame, according to WalletHub's latest Hedge Fund Report -- along with some key trends.

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What are billionaires buying and selling now?

Here are the 10 stocks billionaires and hedge fund managers bought the most of during the fourth quarter of 2017.

Rank Company (Stock Symbol) 1 Apple (NASDAQ: AAPL) 2 Fortive (NYSE: FTV) 3 Aptiv PLC (NYSE: APTV) 4 Nike (NYSE: NKE) 5 Bank of America (NYSE: BAC) 6 Comcast (NASDAQ: CMCSA) 7 Microsoft (NASDAQ: MSFT) 8 Wells Fargo (NYSE: WFC) 9 Verizon (NYSE: VZ) 10 General Electric (NYSE: GE)

Data Source: WalletHub Hedge Fund Report.

And here are the 10 stocks they're selling the most of:

Rank Company (Stock Symbol) 1 International Business Machines (NYSE: IBM) 2 Amazon.com (NASDAQ: AMZN) 3 Facebook (NASDAQ: FB) 4 Aetna (NYSE: AET) 5 Boeing (NYSE: BA) 6 Celgene (NASDAQ: CELG) 7 JPMorgan Chase (NYSE: JPM) 8 Alphabet (NASDAQ: GOOGL) (NASDAQ: GOOG) 9 The Home Depot (NYSE: HD) 10 Citigroup (NYSE: C)

Data Source: WalletHub Hedge Fund Report.

That's the data, based on WalletHub's analysis of SEC filings from more than 400 of the largest U.S. hedge funds and billionaire investors.

While there are tons of possible conclusions that could be drawn from this data, here are just a few key observations.

Cashing out of FANG stocks?

"FANG stocks" refers to four of the biggest names in tech -- Facebook, Amazon, Netflix, and Google (now Alphabet, but FANA simply doesn't sound as cool).

Not only are the FANG stocks some of the most popular in the market, but they have also been some of the best performers. While the S&P 500 has increased by about 30% over the past three years, all of the FANG stocks have handily outperformed it. In fact, Netflix and Amazon have each increased by about 10 times as much as the S&P.

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AMZN data by YCharts

It appears that hedge fund managers may be cashing in their gains. Three of the four FANG stocks (Amazon, Facebook, and Alphabet) are among the most-sold stocks, while none are among the most widely bought.

Buffett's moves are usually the largest

Another thing to notice is that the stock moves of Warren Buffett-led Berkshire Hathaway (NYSE: BRK-A) (NYSE: BRK-B) are usually some of the biggest among all billionaires and hedge funds. Simply put, Berkshire's stock portfolio is massive, and it's not a stretch for Buffett and his team to invest (or dispose of) billions of dollars worth of a single stock.