As of July, the 50 Shades trilogy had sold 20 million copies in the United States, with sales roughly split between print and digital formats.

The Bookseller says that 50 Shades of Grey has sold 3.8 million copies in print according to Nielsen BookScan, which would suggest 1.5 million ebooks sold. (An earlier version of this article suggested that those were the actual sales figures, but Random House UK would not confirm them.) That actually means it’s sold fewer print copies than J.K. Rowling’s Harry Potter and the Deathly Hallows, which sold 4 million copies in print. The Harry Potter ebooks were not available until this year, and Rowling is selling them separately through her own website, Pottermore.com — so we don’t yet have a comparable figure for how many  copies a single Harry Potter title has sold in both print and digital formats. (I’ve asked Pottermore if they can share any information.)

E.L. James published the 50 Shades trilogy with a small Australian publisher before the rights were snapped up by Random House on both sides of the Atlantic in April. The books started out as Twilight fan fiction posted in full on FF.net. The three ebooks had sold over 250,000 copies together and hit the top spots on the New York Times ebook fiction bestseller list before Random House bought the rights. Random House UK is not including those 250,000 copies in its overall sales figure. It’s unclear if Random House UK is including those earlier ebook sales in its figure, and I’ve asked for clarification.

Separately, Amazon announced this week that E.L. James is “the #1 bestselling author of all time at Amazon.co.uk, eclipsing J.K. Rowling’s total sales.” Amazon said James has sold over two million ebooks at Amazon UK since April.

Vintage paid seven figures to republish E.L. James’ 50 Shades of Grey trilogy, which was first published in book form last year by a small Australian publisher. Before that, the trilogy appeared in a slightly different form, under the title Master of the Universe, on fan fiction site FF.net.

Sarah Weinman at Publishers Marketplace reported yesterday (subscription required) that Vintage publisher Anne Messitte called 50 Shades of Grey and Master of the Universe “two distinctly separate pieces of work.”

Today Jane Litte, who runs the popular romance blog “Dear Author,” compares 50 Shades of Grey to Master of the Universe using a variety of Internet tools, and finds that the works are quite similar — 89 percent the same, according to plagiarism-detection tool TurnItIn.

“With the success of Alternate Universe fan fiction and the successful leveraging of that fandom into seven-figure economic rewards, the influx of fan fiction into professional publishing is likely to begin at greater levels than previous,” Litte writes. She says it’s important to state a book’s provenance: “It’s an indicator to readers that they may have encountered this before and it gives the fandom that propelled the author to success a nod. At the very least it’s courteous. At the most, it’s truthful advertising.” She’ll be running a series of posts on fan fiction and copyright, and I’m looking forward to reading them.

The fact that 50 Shades of Grey is extremely similar to Master of the Universe, a work that was previously free online, is not the only issue here. To me, the fact that Master of the Universe was once free and available isn’t that problematic: Many people who are reading the book now would never have encountered it in its previous form online; there’s value in packaging something into a print or e-book (people still pay for print copies of Pride and Prejudice even though that’s a public-domain work free in its entirety on the Internet); and honestly, if a publisher can get readers to pay, more power to ‘em.

For me, one question is: How similar is 50 Shades of Grey to Twilight (not very unless Twilight contains a major bondage and sadomasochism element that I missed)? All sorts of works take inspiration from other works — everything from the movie Clueless (based on Jane Austen’s Emma) to books like Wide Sargasso Sea and The Hours. (Twilight is a lot more recent than Jane Eyre and Mrs. Dalloway, of course — its author is still alive and writing — and that makes things a little more complicated.)

More importantly, as more fan fiction gets monetized in book form, will other copyright issues arise? At “Dear Author,” commenter Merrian writes, “What we risk missing is considering and building some consensus about what is fair use and what is the ethical way of going about using fan fiction outside the realms of creating and making it because work that arises in fandom’s often has a collaborative and shared conception.”

50 Shades of Grey is the first title in a trilogy by British author E. L. James. This morning, the NYT reports (in what is currently the most-emailed article on the site) that the book has “electrified women across the country, who have spread the word like gospel on Facebook pages, at school functions and in spin classes…conversation about the book online has fed many of the sales.” Over 250,000 copies have been sold.

Though the NYT mentions the “word-of-mouth excitement” the trilogy has generated and says James “began the trilogy by posting fan fiction online,” the article doesn’t explain its origins in detail. Well-known romance blogs like “Dear Author” and “Smart Bitches, Trashy Books” have been covering 50 Shades of Grey since last year. 50 Shades of Grey is hugely popular on social reading site GoodReads, where it was a finalist for “Best Romance” in the 2011 GoodReads Choice Awards. There, it has been rated 6,821 times (with an average star rating of 4.34) and reviewed 1,347 times.

The trilogy was published last year by a small Australian company, Writer’s Coffee Shop Publishing House. Random House’s Vintage announced today that it paid seven figures for the print and digital rights to the trilogy at auction. The Random House e-book will be available Monday, and a 750,000-copy print run of a redesigned paperback edition will follow. (You can buy the e-book on Kindle and Nook for $9.99 now, but it is still the Writer’s Coffee Shop edition, though the publisher is listed on Amazon as Random House.)

“Dear Author” founder Jane Litte explains the trilogy’s origins:

It was originally published along with the two sequels, Fifty Shades of Darker and Fifty Shades of Freed, in its entirety, as Master of the Universe on ff.net, a site that hosts what is known as fan fiction. Master of the Universe reimagined the Bella and Edward love affair set in contemporary Seattle, Washington with Bella as the young college graduate virgin and Edward as the masterful billionaire with secret sexual predilections. This collection of submissions has since been deleted.

She also notes “During the height of its popularity, an auction for the series raised $30,000. The author appeared on a fan fiction panel at the 2010 ComicCon and attended a three day conference in DC thrown by her fans.”

And at Smart Bitches, Trashy Books, Sarah Wendell explains why she thinks the book became so popular:

It has a secrecy element, for example, similar to some paranormal romances and their avid fanbases. It’s also not at all surprising that 50 Shades and Twilight share a few plot themes, specifically that secrecy and the temptation inherent in the world of both narratives, and the alpha male who is opulently, ridiculously wealthy, Volvos optional. Plus, Edward, as I wrote a few years ago, and in many similar ways (again, surprise surprise) Christian are both very much old-skool-style romance heroes. 50 Shades (and Twilight, obviously) are also told from the heroine’s POV, a very deep, first person, detail-heavy point of view, and the narrative is also akin to reading a diary, adding to that sense of illicit secrecy.

But the point of divergence between them is that secret — and this is not to say that at this point 50 Shades become a wholly original piece of fiction. It is not, considering how much of the character types are based on Stephenie Meyer’s work….

Ultimately, I think 50 Shades is popular because of the combination of elements and the foundation it “borrows” from Twilight, among them the very mysterious and barely glimpsed alpha-male point of view, and the presence of a very innocent heroine being inducted into a secret, sexually charged environment. Moreover, the scarcity of paper copies and the absorbing qualities some readers find in the story, as well as their own reactions and desire to share the recommendation with others in an exclusive environment, contribute to the increasing coverage.

Twimore.com was launched by Kaleb Nation, the 22-year-old author of the extremely popular Twilight fan blog TwilightGuy.com. Nation blogged about his experience as a guy reading the Twilight novels between 2008 and 2009; since he finished them, he’s turned the site into a legitimate and well-known source of Twilight book and movie news. That’s all to say that Twimore.com is a parody created by a fan, not a hater, and the most interesting thing about it isn’t that it’s funny (though it is) but that it hints at pent-up demand for other author-driven fan communities.

A lot of fans thought that Nation’s video parodying J. K. Rowling’s original announcement about Pottermore.com was real–as did Pottermore fans who were incensed that Stephenie Meyer would dare to copy Rowling so blatantly. That’s despite the fact that Stephenie Meyer does not appear in the video at all except in a Photoshopped screenshot. It’s narrated by Nation, who describes Twimore at one point as “something that’s never been done before, in any fandom, EVER, in the history of time…Twimore is open to everyone, immediately. Simply…follow the sparkles. Or just go to Twimore.com. I don’t care.”

“CHEATER YOU BLOODY FILCH!! SHE IS RIPPING OFF OF POTTERMORE!!!!! PROOF WHAT WITH JACOB BLACK BEING A RIP OFF OF SIRIUS BLACK AND ALL!!!!!” wrote a commenter in one of 982 comments posted on YouTube (NSDQ: GOOG). Even those who realized it was a parody were angry: “OK I know it’s a joke, but if one day Stephenie Meyer JUST TRY to make a ‘Twimore’, I swear I’ll hunt her and eat her bones. Or just scold her a lot in Twitter. HARRY POTTER RULES!” wrote another.

The lesson for Stephenie Meyer and other popular authors with avid/rabid fan bases? Don’t copy Pottermore (she, and most other authors, don’t hold their own e-book rights anyway), but see what you can learn from it and don’t underestimate the power of matching fans with special “vampire names.” Also, stay away from that bone-eating Harry Potter fan.