The Secret keeps on spreading. Two millions additional copies have been ordered for Rhonda Byrne's self-help phenomenon, yet another beneficiary of Oprah Winfrey, who devoted two shows to the book in early February. Released last fall by Atria Books, an imprint of Simon & Schuster, The Secret now has 3.75 million copies in print and for days has displaced the final Harry Potter book, "Harry Potter and the Deathly Hallows," from the top of Amazon.com, where "The Secret" is currently out of stock.

"It is a testament to the powerful attraction of The Secret that it has been selling out faster than we can supply it to our customers," Judith Curr, Atria's executive vice president and publisher, said Thursday in a statement. The audio book, a four-CD set, is also selling fast, with 400,000 copies in print, according to Atria, which describes The Secret as containing "wisdom from modern-day teachers -- men and women -- who have used it to achieve health, wealth, and happiness."

Created by Australian producer Byrne, The Secret began as a DVD film, released last March and, thanks to aggressive Internet marketing, became enough of a hit to be spun off into a book, which Byrne finished in less than a month.