As of January 18th, it appears the texts have been taken down off the Barnes & Noble website. But prior to that you could have downloaded instructions for how to make a pressure cooker bomb, similar to the ones used in Boston several years ago.

According to the website PJMedia, the instructions were contained inside several editions of the Al-Queda propoganda magazine Inspire, which debuted in 2010. It was their first English-language propoganda offering. PJMedia says they have been on the bookseller's website for years. Inspire is apparently their attempt to persuade people to 'come over' to their line of thinking.

According to the source, instructions were included in some of the texts, including a passage called "Make a Bomb in the Kitchen of Your Mom."  It contained explicit directions on what easily attainable materials could be used to turn a pressure cooker into a bomb, including how to fit it with a timer.

The text also said such weapons were preferable to pipe bombs, because they cause more damage and loss. These were the type of weapons used in the Boston Bombings.

However, after the PJ story broke, the items have been taken down from the bookseller's website.  No official comment was issued by Barnes & Noble, but some experts are saying it was likely the result of an oversight--that nobody carefully checked the Al-Queda text for any harmful or terrorist-type activities or instructions.