Jessikka Aro, a Finnish journalist who's been the subject of a sustained attack by Russian propaganda trolls ever since she started investigating them. Last spring someone sent her a text message pretending to be from her father – who died 20 years ago – telling her he was "watching her". Another wrote a song, mocking her as a bimbo "James Bond" NATO agent with a drug habit. There is even a music video online, with Aro portrayed by an actress in a leotard and wig. It would be funny if it wasn't dripping with venom. And just a few weeks ago there was a blog post. Someone had trawled through old court records and found a copy of Aro's 12-year-old fine for amphetamine possession, twisting it into outrageous claims of addiction and drug dealing. Personal attacks on journalists are nothing new. But the case of Jessikka Aro is considered extraordinary by European Union officials familiar with this and other cases.

Part of the online trolling used against Finnish journalist Jessikka Aro. They told Fairfax Media it was a case study of Russia's escalating "information war" against the West, an increasingly sophisticated and well-resourced operation that already counts the annexation of Crimea among its successes. Aro is an investigative journalist with Finnish Broadcasting Company Yle. All her life she has been fascinated by Russia, she says – "it's my favourite topic, really" – she finds Russian society "interesting, fascinating and also a bit scary". Finland's history makes its bigger, stronger neighbour an enduring presence in its culture and politics. Aro had been writing about jihadist propaganda, and noticed reports about Russia's "troll factories", reportedly Kremlin-funded set-ups pumping out fabricated news and propagandist social media commentary: regurgitated misinformation from the bowels of the internet.

All these horrible things [they say] have given me this feeling of fear sometimes. They stalk me all the time. They stalk everything that I do on social media. Jessikka Aro So in September 2014 she crowdsourced an article, asking Finns "to help look for trolls, [tell me,] how do the trolls act, how do they work, what is their influence in Finnish public opinion? "I got something like 200 responses and information," she says. "I also got so much trolling." A few days later Finnish pro-Russian activist Johan Backman got involved. Last year he was appointed the "official representative" of the Russian Institute for Strategic Studies in the Nordic countries. RISS was founded by Russian President Vladimir Putin, as a think tank/lobby group funded by the Kremlin to promote its policies and interests, domestically and in Bulgaria, Turkey, Finland and France. But Aro says Backman was doing more than just disagreeing with her journalism.

"He started to fill the internet ... with disinformation about me being some kind of helper of the United States and Estonia and other countries' intelligence services or security and police services," Aro says. "[He was] claiming – lying – that I am collecting some kind of illegal database of Putin supporters in Finland. And that it's criminal. "He was doing very active campaigning against me." Fairfax Media put a list of questions to Backman but he had not responded at the time of writing. According to a report from a Finnish news agency, police last week launched an investigation into Backman and the chief editor of a news blog, MV Online, in relation to the persecution and defamation of Aro. Backman stirred up the trolls, Aro says. Soon after she began to receive "very disturbing messages, absurd messages, trolling messages" in Russian, English and Finnish, on the internet and by phone. And over time – as she has written more stories about their activities – they have just become worse.

"All these horrible things [they say] have given me this feeling of fear sometimes. They stalk me all the time. They stalk everything that I do on social media. They take my pictures and add them to [false blogs]." They "repurposed" her holiday photos, they emailed editors and politicians to call for her sacking. They even stalk her friends. At one point, one offered to "play down" the hate speech against her if she apologised and promised to stop writing about pro-Russian trolls – an offer Aro considered blackmail. Such trolls, Aro says, are having an unhealthy impact on freedom of speech and democracy more broadly. Aro says she has spotted some "high-profile officials" in the Finnish parliament lurking on troll groups on social media.

And she says ordinary Finns who are exposed to troll misinformation have "told me that they have started to lose touch with what is true and what is not true ... for example, in the Ukraine crisis they don't know what is a fact and what's not, because trolls mess up the conversation". Some of those attacking her say they are just exercising freedom of political speech. Aro has no time for that argument. In fact they are trying to suppress other people's free speech through aggression, she says. An EU official who has been studying Russian propaganda – and who spoke to Fairfax Media on condition of anonymity – says Aro's case is "quite extraordinary". "I'm actually surprised this is happening in the EU," he says. The amount of resources being put into an attempt to bully Aro was remarkable. "Not only money but also people. The purpose: intimidation ... to kill the debate."

However, Aro is far from the only victim, nor the only topic of pro-Russian trolling, misinformation and propaganda, the official says. "You go through the disinformation stories around the continent and you see the very same article launched at some minor Russian blog site, then multiplied by 15, 20 different web pages and then gets back to the Russian media who can say, 'Oh, ISIS fighters have joined the Ukrainian armed forces.' "It is organised to serve the purposes of the Kremlin." The official says the propaganda takes different forms in different countries: in Britain it exploits the Brexit issue, in the former Soviet bloc it tries to drive a wedge between countries over Middle Eastern refugees. Prior to Russia's annexation of Crimea, the official says, a flood of disinformation clouded claims that Russian troops had entered the Ukraine province.

"It showed that disinformation can affect our political decision-making," he says. More recently, a claim emerged – since admitted false – that a 13-year-old Russian-German girl was raped by a Middle Eastern or North African refugee in Berlin. The claim was spread and outrage stoked by pro-Russian trolls, even sparking a protest on the streets of Berlin, and then was stirred further by the Russian Foreign Minister before the whole story was found to be a hoax. "This is a serious problem that doesn't just affect the Ukraine or Baltic states but also a huge part of Europe," the official says. He puts credence in a theory that the troll network is used to "road-test" conspiracy theories, seeding six or seven competing pieces of propaganda or misinformation and letting the Darwinian world of online information exchange prove which is the hardiest – which is then republished by more conventional media. It's a system applied, for example, to the shooting down of Malaysia Airlines flight MH17 in 2014. "One of the biggest problems is we don't have a clue how much money they put into this," the official says. "We do not have clue how much media there are, how many people they target, how many people they reach. We can only guess from the results.