The Harry Potter novels have been put on sale as audio downloads in a bid by author JK Rowling to tackle piracy.
Author JK Rowling's audio books have sold more than 5m copies
All six books, including the most recent release Harry Potter and the Half-Blood Prince, can now be purchased in the US via Apple's iTunes site.
Rowling sanctioned the move after fans reported online bootleg editions.
"Apart from the fact that they are illegal, the Potter content of these can bear very little resemblance to anything I've ever written," she said.
In a message posted on her website, Rowling said she was concerned about online piracy.
"Many Harry Potter fans have been keen for digital access for a while, but the deciding factor for me in authorising this new version is that it will help combat the growing incidents of piracy in this area," Rowling wrote.
The author had previously only permitted paper and traditional audio releases, making her work a target for online pirates, although illegal sales were believed to have been relatively small.
The Potter books can now be bought as audio downloads, either individually or at a one-off price for the entire set.
The first five books are available in the UK, with the sixth following on 11 October.
Meanwhile, Rowling has accused eBay of failing to take responsibility for bootleg Potter items sold on the online auction site.
She said on her website that she was concerned by a wave of Potter merchandise with fake autographs up for sale on eBay.
"As far as I could tell on the day I dropped in, only one of the signatures on offer appeared genuine," she wrote.
"There seem to be a lot of people out there trying to con Harry Potter fans.
"The same is true in respect to the huge number of unauthorised Harry Potter e-books and audio digital files that users of eBay have offered for sale to Harry Potter fans."
A spokesman for eBay, Hani Durzi, said Rowling was part of a copyright protection scheme offered to allow members to report problems among the estimated 55 million listings.
"It's the responsibility of the copyright owner to report any listings that violate their rights," he said.
"When they do, we take those listings down immediately."