David Tepper, head of $20 billion Appaloosa Management, cut his SPDR S&P 500 ETF stake by over 6 million, to 4,814,613 shares, according to a 13F filing with the SEC. 

Still, that ETF represents the largest single holding in the the filing, valued at $900 million as of the end of March 31.

His second largest holding was PowerShares QQQ Trust, which tracks the Nasdaq. That position was worth $815 million.

Speaking at SALT conference in Las Vegas on Wednesday, Tepper said he is "nervous," that the stock market is "getting dangerous" and that he's not saying go short, but "just don't go too friggin long."

Tepper added brand new positions in Facebook (478,500 shares), Expedia (695,837 shares) and Priceline (183,224). Halliburton is one of his top position increases with 4,032,021 new shares to bring his position as of March 31 to 5,024,621.

He liquidated his positions in Transocean, Foster Wheeler, EMC Corp, Hartford Financial, Fluor. Tepper also sold 2.8 million shares in MGM Resorts International and now has 3,598,758 shares. 

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