“Mein Kampf” was one of the best selling e-books of 2013.

The Hitler manifesto rose to the top of the charts last year, ranking number one on Amazon’s propaganda and political psychology section. It also ranked 12th and 15th in the politics and current events sections on the iTunes bookstore.

Despite its electronic success, the book has been stagnant in the printing world for years. Insiders are saying the discrepancy could come from the anonymity e-books provide.

“These are things that people would be embarrassed to read otherwise,” journalist Chris Faraone, who first wrote about the movement, told ABC News.

“Books that people would probably be a bit more embarrassed to read or display or buy in public, they are more than willing to buy on their Kindle, or iPads.”

On news site Vocativ, Faraone further explained the surprising trend:

On Amazon, there are more than 100 versions of Mein Kampf for sale in every conceivable print and audio format, from antique hardbacks to brand-new paperbacks. Of those 100 iterations, just six are e-books—yet all six of them rank among the 10 best-selling versions overall. And those are just the ones people are paying for.

“Mein Kampf” first became available electronically in 2008, according to Faraone.