NEW YORK ( TheStreet) - Greenlight Capital hedge fund manager David Einhorn evidently has faith in Yahoo! ( YHOO) CEO Marissa Mayer.

Among the many moves revealed in Einhorn's latest 13F filing, is the initiation of a hefty position of roughly 4 million Yahoo! shares during the third quarter.

Elsewhere, Greenlight was found to have lightened investments in names such as Apple ( AAPL), Microsoft ( MSFT), and Seagate Technology ( STX) during the quarter.

Einhorn cut his stake in Apple to 1.09 million shares as of Sept. 30 from 1.45 million at the end of June.

Greenlight's exposure to Seagate saw a deep cut, going to 16.6 million shares from 23.2 million. Einhorn liquidated holdings in Microsoft options, but kept his nearly 7.3 million share stake in the company.

Einhorn, who touted General Motors at an investment conference in October, added to his stake in the Detroit-based automaker during the third quarter, going to 21.6 million shares from 17.4 million.

In addition to Yahoo!, Einhorn initiated new positions in names such as Babcock & Wilcox ( BWC) and Aecom Technology ( ACOM). Einhorn had owned shares of Yahoo! in the past but traded out as his thesis changed under former CEO Scott Thompson.

Interested in more on Yahoo!? See TheStreet Ratings' report card for this stock.

-- Written by Chris Ciaccia in New York

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