A funny thing happened on the way to this column. Browsing idly through the Publishers Weekly site, I came on the list of the Nielsen bestselling books of 2014 (so far) in the US. The Top 20 list was dominated by "young adult" fiction, books such as Divergent by Veronica Roth and John Green's The Fault in Our Stars, plus the usual movie tie-ins. At No 9 ,there's a religious book, Jesus Calling: Enjoying Peace in His Presence by missionary Sarah Young. At No 11 is Heaven is for Real ("A little boy's astounding story of his trip to Heaven and back").

Two slots further down there's a "junior novelisation" of the Disney film, Frozen. At No 15 is an "activity book", complete with 50 stickers, based on the same film.

At this point, your columnist was losing the will to live. Is this, he wondered, what a free society really chooses to read? But what's this? At 16 and 17 there are two computer game manuals – Minecraft: Redstone Handbook and Minecraft: Essential Handbook.

The only people in your household who will be astonished that two computer game manuals are selling like hot cakes are the adults. This is because they don't know what every child from the age of six upwards knows, namely that Minecraft is the most absorbing and intriguing gaming idea since David Braben and Ian Bell created Elite in 1984.

What's even more astonishing (for adults anyway) is that Minecraft has none of the CGI faux-realism of the blockbuster computer games marketed by Electronic Arts et al. Players are not compelled to act out the crazed, violent, misogynistic scripts dreamed up for them by programmers working for multimedia conglomerates. In Minecraft, there's no realism and no script.

Instead, you find yourself in a virtual world made of 1x1 blocks. The analogy with Lego is unmistakable, but the Lego corporation had nothing to do with Minecraft. The virtual world has mountains, valleys, lakes and clouds, but the version of it in which you find yourself is uniquely yours – it's generated by an algorithm.

And you are dropped into it with no instructions. So you spend the first few hours simply exploring it as a virtual tourist. And you find that you can do things with blocks, such as build a wall or make a cave.

But then you notice that the light fading (a Minecraft days lasts only 20 real-time minutes) and all of a sudden you are transformed from blithe tourist into frightened rabbit. Because in Minecraft the night is full of horrors – spiders, skeletons, zombies and camouflaged creepers, all of which have an eerie ability to pursue you relentlessly and remorselessly. And the only way to stay safe is to build yourself some kind of shelter or dig out a cave in which to wait out the hours of darkness.

With experience, you figure out ways of coping. You learn how to build elaborate structures and acquire skills that enable you to fashion weapons with which to combat the terrors of the night. And you can build anything you like, as long as it can be made out of blocks, which means that some people have built replicas of the Taj Mahal. Again, the analogy with Lego is compelling.

What happens if you don't know how to build something? Answer: go to YouTube and type "Minecraft how to build…"

And at this point you begin to appreciate the extent of the Minecraft phenomenon, because the number of people who have proudly explained in video how they constructed this or that in the game is staggering.

But the most implausible thing of all is that this ostensibly simplistic and unrealistic game currently has more than 40 million players worldwide, many of whom are fanatical in their devotion to it. And it was created not by some large multimedia corporation but by a single Swedish programmer, Markus Persson, who has made hundreds of millions of dollars from it, and who is regarded by Minecraft players with the kind of awed respect that Linus Torvalds is accorded by users of the Linux operating system.

The Minecraft phenomenon runs counter to almost every trend in the contemporary computing industry, which is towards the kind of consumer lock-in and corporate control that we see in the "normal" games industry, in which teenagers frenziedly play a new game for a few weeks and then drop it. And perhaps therein lies the secret of Minecraft's attraction: it's open-ended. Players' possibilities are bounded only by the limits of their imaginations – or by the limits of their knowledge. Which perhaps explains those book sales.