Brown's previous books "The Da Vinci Code" and "Angels & Demons" were blockbusters that were adapted as hit movies.
Knopf Doubleday Publishing Group told The New York Times it is printing another 600,000 copies of "Symbol" after more than 1 million hardcover and e-book versions were sold Tuesday.
The publisher's first run of the thriller was 5 million copies.
Attkisson leaves CBS News, reportedly over network's 'liberal bias'
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