WH Smith was quick to remove DIY terror manuals from the digital shelves of its online stores after El Reg highlighted their sale but other retailers have demonstrated less of a knee-jerk reaction.
A fortnight ago the Brit book and stationary outlet shuttered its website for emergency maintenance to remove books including the Improvised Munitions Handbook, and companion reads Boobytrap, and Explosives and Demolitions.
The retailer's coders scrubbed certain listed titles over the space of four hours and created filters so the books did not appear for sale again from automated feeds of book wholesalers' catalogues.
All three titles have since continued to be stocked by Apple's iBook Store, along with other similarly themed publications including 100 Deadly Skills – both the standard and the survival editions listed.
"To protect freedom of speech and avoid censorship, unless a title is illegal we tend not to remove it from the iBooks Store," a representative at Apple told The Register.
Over at the UK's largest native book seller Waterstones, the Improvised Munitions Handbook no longer appeared to be available when we looked, but Boobytrap still was.
A spokesman for Waterstones said it does amend the automatic feed to "eliminate, as far as we are able, pornographic or other objectionable titles" but added: "We do not eliminate books of the sort you highlight on grounds of common sense. The authorities may stop their publication with ease should they judge this necessary."
Amazon sells a range of how-to books including Forbidden Knowledge, the US Army Guerrilla Warfare Handbook, and The Anarchist Cookbook. Amazon said: "Thanks for the opportunity but we will decline to comment."
Obviously, most terrorists are unlikely to use any of these store fronts to buy how-to guides on bomb-making etc. Those that don't have a background in such things will likely browse the content online with protected connections.
But there have been historical examples of the law getting involved. A book shop in Birmingham, Maktabah al-Ansar, was raided in January 2007 and forced to pull down the shutters after it was found to be selling jihad-related titles, and in September that year, an 18-year-old London student was jailed for possessing similar books.
And Thomas Mair, the convicted murderer of MP Jo Cox, was thought to have purchased the Improvised Munitions Handbook from a US source. This book "demonstrates... techniques for constructing weapons that are highly effective". Mair shot Cox with a homemade gun.
El Reg asked the Home Office if book sellers had a duty of care to prevent such materials being sold in store – even when they are freely available to download online. The department refused to comment.
It is an offence under section 2 of the Terrorism Act 2006 for someone to "disseminate a terrorist publication with the intention that it will encourage or assist terrorism, or if they are reckless as to whether it will do so".
But it is for the cops to probe suspected offences in individual cases and for the Crown Prosecution Service to determine prosecutions.
The Metropolitan Police Service said it had received no reports relating to the Handbook or other related titles, adding that: "Any report would be carefully reviewed and a decision made whether action is required." ®