One explanation offered for the surge in electronic sales concerns the relative anonymity offered by e-books as compared to their printed counterparts.

“These are things that people would be embarrassed to read otherwise,” journalist Chris Faraone, who spotted the trend 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.”

Faraone believes the phenomenon is similar to that surrounding erotic novel “Fifty Shades of Grey,” which in 2012, became the first to sell more than 1 million copies on Amazon’s Kindle e-reader.

“’50 Shades of Grey’ is something you would probably be embarrassed to read in public,” said Faraone, but added that the anonymity offered by e-readers ensures that readers with a latent interest in controversial subject matter can read the books freely without arousing suspicion.