The thing that Margo Gontar found easiest to deal with were the dead children. They were all over her computer screens – on news sites and social media – next to headlines that blamed the deaths on Ukrainian fascist gangs trained by Nato. It was early 2014, Crimea had just been taken over by soldiers who seemed Russian and sounded Russian but who were wearing no national insignia, and who Vladimir Putin, with a little grin, had just told the whole world were not Russian at all. Now eastern Ukraine was being taken over by separatists. Gontar was trying to fight back.

She could usually locate the original images of the dead with a simple Google search. Some of the photographs were actually from other, older wars; some were from crime scenes that had nothing to with Ukraine; some even came from movies. Gontar posted her research on a myth-busting website called StopFake, which had been started in March by volunteers like her at the journalism school of Mohyla University in Kiev. It felt good being able to sort truth from lies, to feel some kind of certainty amid so much confusion.

But sometimes things could get more complicated. Russian state-television news began to fill up with plump, weeping women and elderly men who told tales of Ukrainian nationalists beating up Russian-speakers. These witnesses seemed genuine enough. But soon Gontar would see the same plump women and the same injured men appearing in different newscasts, identified as different people. In one report, a woman would be an "Odessa resident", then next she would be a "soldier's mother", then a "Kharkiv resident" and then an "anti-Maidan activist".

In July, after the downing of Malaysia Airlines flight MH17 over eastern Ukraine, Gontar surveyed the internet, picking up shards of pro-Russian conspiracy theories. She came across the Twitter feed of an air-traffic controller who had spotted Ukrainian army jets following the plane, although she could find no evidence that the air-traffic controller actually existed. She found dozens of sites in Russian and English which, almost as one, suddenly argued that the US had shot down MH17 in a botched attempt to target Putin's personal jet. There were even claims, circulated by Russian separatist leaders in Ukraine, that the plane had been filled with corpses before it had taken off – a plotline lifted from the BBC TV series Sherlock. The stories were glaringly sloppy, as if their creators did not care about being caught and just wanted to distract from the evidence that Russian-backed militias had shot down the plane. Gontar began to wonder whether she was falling into the Kremlin's trap by spending so much time trying to debunk its obviously fake stories.

Before long, she found herself, and StopFake, becoming part of the story. Russian media had begun to cite StopFake in their own reports – but would make it look like Gontar was presenting the falsified story as truth, rather than debunking it. It was like seeing herself reflected in a mirror upside down. She felt dizzy.

At times like this, she had always reached out to western media for a sense of something solid, but this was starting to slip too. Whenever somewhere like the BBC or Tagesspiegel published a story, they felt obliged to present the Kremlin's version of events – fascists, western conspiracy, etc – as the other side, for balance. Gontar began to wonder whether her search for certainty was futile: if the truth was constantly shifting before her eyes, and there was always another side to every story, was there anything solid left to hold on to?

After months working at StopFake, she began to doubt everything. Who was to say that "original" photo of a dead child she found was genuine? Maybe that, too, had been placed there? Reality felt malleable, spongy. Whatever the Russians were doing, it was not simply propaganda, which is intended to persuade and susceptible to debunking. This was something else entirely: not only could it not be disproven, it seemed to vaporise the very idea of proof.

* * *

Late last year, I came across a Russian manual called Information-Psychological War Operations: A Short Encyclopedia and Reference Guide (The 2011 edition, credited to Veprintsev et al, and published in Moscow by Hotline-Telecom, can be purchased online at the sale price of 348 roubles). The book is designed for "students, political technologists, state security services and civil servants" – a kind of user's manual for junior information warriors. The deployment of information weapons, it suggests, "acts like an invisible radiation" upon its targets: "The population doesn't even feel it is being acted upon. So the state doesn't switch on its self-defence mechanisms." If regular war is about actual guns and missiles, the encyclopedia continues, "information war is supple, you can never predict the angle or instruments of an attack".

The 495-page encyclopedia contained an introduction to information-psychological war, a glossary of key terms and detailed flowcharts describing the methods and strategies of defensive and offensive operations, including "operational deception" (maskirovka), "programmatical-mathematical influence", "disinformation", "imitation", and "TV and radio broadcasting". In "normal war" the encyclopedia explains, "victory is a case of yes or no; in information war it can be partial. Several rivals can fight over certain themes within a person's consciousness."

I had always imagined the phrase "information war" to refer to some sort of geopolitical debate, with Russian propagandists on one side and western propagandists on the other, both trying to convince everyone in the middle that their side was right. But the encyclopedia suggested something more expansive: information war was less about methods of persuasion and more about "influencing social relations" and "control over the sources of strategic reserves". Invisible weapons acting like radiation to override biological responses and seize strategic reserves? The text seemed more like garbled science fiction than a guide for students and civil servants.

Information war was less about methods of persuasion and more about "influencing social relations"

But when I began to pore over recent Russian military theory – in history books and journals – the strange language of the encyclopedia began to make more sense. Since the end of the cold war, Russia had been preoccupied with the need to match the capabilities of the US and its allies. In 1999, Marshal Igor Sergeev, then minister of defence, admitted that Russia could not compete militarily with the west. Instead, he suggested, it needed to search for "revolutionary paths" and "asymmetrical directions". Over the course of the previous decade, Russian military and intelligence theorists began to elaborate more substantial ideas for non-physical warfare – claiming that Russia was already under attack, along similar lines, by western NGOs and media.