The warning comes amid fears of Russian interference in upcoming national elections in the Netherlands, France and Germany.
On Friday, it also emerged that Russia is now suspected by Italian officials of being behind a sustained hacking attack against the Italian foreign ministry last year that compromised email communications and lasted for many months before it was detected.
An Italian government official said the attack took place last spring and lasted for more than four months but did not infiltrate an encrypted system used for classified communications.
The hacking is now the subject of an inquiry by the chief prosecutor in Rome.
The latest revelation of Russian hacking comes amid heightened concerns that Moscow has targeted Nato members, including the US, France, Germany, the Netherlands and Bulgaria, as part of a cyber campaign that seeks to weaken the governments of those countries and disrupt critical infrastructure.
In the US, intelligence agencies have blamed Russian government-sponsored hacking groups for breaching the Democratic National Committee and officials in Hillary Clinton's campaign during the 2016 presidential elections, in part to try to help Donald Trump win the White House.
In an interview with this website, John Duhig, a senior counsellor with the Brussels-based European Foundation for Democracy, said, "Promoting propaganda and fake news are not new phenomena.
"However, with the allegations of Russian government interference in the 2016 US presidential elections and the growing perception that ISIS is a creation of Western governments, a quite different - and subversive - narrative has gained traction across parts of the Middle East/ North African region. This new reality becomes the truth for many."
Duhig added, "Any country can be more or less vulnerable to cyberattacks and other illegal infiltration activities, however, open, democratic western systems are by definition vulnerable to propaganda and the spread of fake news from unscrupulous groups, terrorist organisations or authoritarian regimes that do not operate within the rule of law.
"Western governments face an existential challenge to protect the integrity of our democratic systems and voting structures without resorting to similar illegal activities. Faith and trust in the fundamental precepts of democracy must be maintained, but not at any cost."
He said, "EU member states, as well as Nato, are not only investigating any cybersecurity weakness within our complex systems, but also looking at how the propaganda machine, particularly that of Russia, is impacting on public opinion.
"There is widespread concern that Russia has been funding and providing logistical support to populist, anti-EU, anti-western groups and political parties across Europe.
In a situation where terrorism and growing polarisation across Europe is creating fear among the public, national governments, the EU institution and Nato are rethinking how to address this threat."
Duhig said, "As of now they have not come up with an answer and the longer they wait the worse the situation will get."