Novelists are often quiet, retiring and law-abiding, keeping their more audacious ideas and antics for the pages of their books.

Not so Andrew O'Hagan, however, who has stepped beyond the realm of the wholly honest to delve into a dodgy and at times illegal netherworld, all in the name of research.

In a recent essay in the London Review Of Books, O'Hagan describes how it was the sight of headstones for dead children in a London cemetery that inspired him to resurrect a long-dead young man and give him a seemingly real persona, an act of creation only possible in the internet age.

The impetus came in part from the revelation that for years this was what undercover police had been doing in order to create new identities and back stories for their fictitious personas. Taking the details of someone who died as a child, and using their birth certificate to forge new documents in their name, these officers were able to create a convincing character for their alter ego. Only public disgust has brought this practice to a halt, or so we have been led to assume. Such revulsion was no doubt part of O'Hagan's fascination. As he writes, "What was it to use a person's identity - and did anyone own it in the first place?"

The man O'Hagan chose to bring back to life died when he was 20. Ronald Pinn was an east Londoner, who took a heroin overdose. From what O'Hagan was able to glean, he was a decent bloke. Getting hold of his birth certificate was easy, and thereafter O'Hagan created an online presence for Pinn in which he had Facebook and Twitter followers, an email account, and could roam the dark web. Thus he was able to get a bogus degree certificate, a passport and a driving licence, and could buy drugs, as well as trawl gun and weaponry sites with impunity.

O'Hagan drew the line at porn, but by then the point had been made. Already receiving letters from the Inland Revenue, and given a National Insurance number, Pinn was now real, in the sense that any of us in this disembodied virtual world is considered real, until we meet someone face to face. Apparently Facebook estimates that of its 864 million users, around 67 million are fake, while respected companies and organisations create fake digital personalities - digividuals - to influence public opinion.

The twilight realm O'Hagan has illuminated is profoundly disturbing. Novelists are better equipped than most to appreciate the abyss created by the non-existent yet functioning dead, and the potential uses and misuses their presence can be put to. To say it is the stuff of fiction, however, is to have missed the boat. This sort of behaviour has been happening for years. Indeed, one of the fascinating things about O'Hagan's experiment is that it reveals the extent to which most of us are already living in an almost fictional world. The word 'chimera' might be more accurate than fiction, but the distinction is a slim one, in that the line between the real and the illusory is something we are growing used to negotiating or - more dangerously - not even noticing. Without being aware of it, users of social media - and eventually all the rest of us - are open to being manipulated like puppets, our strings tweaked to make us react as some disembodied figure so desires.

It is this aspect of O'Hagan's enquiry that is most alarming, showing how fabricated and unreal parts of our live are becoming, with or without our knowing. It makes fiction as an art form seem quaint, a relict from a more transparent age, when we could all detect the difference between the dead and the living dead, the real and the counterfeit. The emergence of this shadow world raises two immediate questions. First, has the human love of storytelling and make-believe made us particularly vulnerable to this sort of deception? And second, as virtual reality increasingly encroaches upon us, will we lose our appetite for what you might call real fiction, of the old-fashioned, trustworthy sort?