The flags of the EU member states in front of the European Parliament in Strasbourg, France Thomas Trutschel | Photothek | Getty Images

The European Union is having a hard job building a sufficient firewall when it comes to election interference, experts have told CNBC. The European Parliament — the EU's legislative arm — has launched a campaign to tackle online disinformation ahead of its elections in May. But there are certain loopholes that mean there could still be outside influence in the vote. "Russia will attempt to influence the parliamentary elections using its usual tool kit, including targeted propaganda, and the stealing and leaking of information," Andrew Foxall, director of the Russia and Eurasia studies at the Henry Jackson Society, told CNBC via email. He added that there are a number of steps that European institutions should take to prevent such influence. EU countries could share information with each other on "fake news" stories or disinformation; make public any influence attempts — whether from Russia or elsewhere; pledge not to use stolen data in their campaigns and make campaign financing more transparent, Foxall said. The Russian government was not immediately available for comment when contacted by CNBC.

Almost all European populist parties have direct ties to Russia, although this is most often through individual connections rather than institutional ones. Andrew Foxall Director at the Henry Jackson Society

Campaign financing is another sensitive topic in Europe. There is no common European rule for party funding; instead, parties in certain jurisdictions must comply with their country's own rules. "(European) leaders have thus far failed to address a major vulnerability, namely that foreign money can flow unimpeded into campaigns in a number of member states," Kristine Berzina, a senior fellow at the Alliance for Securing Democracy, a national security advocacy group, said in an article last October. According to the International Institute for Democracy and Electoral Assistance, four out of the 28 European countries do not have any restrictions on foreign donations to political parties. They are Belgium, Denmark, Italy and the Netherlands. This means that, for example, an Italian political party could receive funding from a third country, without it being illegal. Eleven other countries have partial restrictions to foreign donations. And only 13 have full bans in place. A spokesperson for the European Parliament told CNBC that the institution contributes to the funding of European political parties through its budget. Up to 85% of party expenditure is reimbursable from the European Parliament , while the rest should be covered by the party's own resources. However, the same spokesperson also said that funding rules for national political parties are outside the European Parliament's remit and as such cannot comment on the matter. European citizens vote on national parties to represent them at the European Parliament. Those elected then decide which European political group they want to be a part of. According to the spokesperson, there is funding for the latter, but no oversight on funding at the national level.

Russian links to European parties

European officials are paying particular attention toward Russia, given the conclusion from U.S. intelligence agencies that the Kremlin did interfere in the U.S. 2016 presidential election. Marine Le Pen's nationalist party, recently renamed National Rally, found itself strapped for cash back in 2014, as none of the French banks wanted to provide it with any loans. But through one of its party members, Jean-Luc Schaffhauser, who had links to the Russian government, Le Pen's party obtained funds from a Russian-based bank, according to the Washington Post. Marine Le Pen has previously denied she has been influenced by Russian money. Furthermore, a former Le Pen advisor, who is currently member of the European Parliament, hired the daughter of President Vladimir Putin's spokesperson, raising some concern along the corridors of the Brussels institution. There have been other episodes showing apparent Russian links with European nationalist parties. Panos Kammenos, the leader of Greece's right-wing nationalist party has often been photographed alongside Russian officials in Moscow. A spokesperson for his Independent Greeks party wasn't immediately available for comment when contacted by CNBC.

Media reports, unverified by CNBC, have also suggested that Italy's Lega, led by Matteo Salvini, sought funding from Russia via a petroleum export deal involving a firm close to the Kremlin. The party has denied the accusations. "Almost all European populist parties have direct ties to Russia, although this is most often through individual connections rather than institutional ones," Foxall told CNBC via email. "These are people who, for example, accept invitations to travel to Moscow or visit illegally-occupied Crimea, both of which are paid for by the Russian state. These same people would also be courted in their home countries by Russian diplomats and intelligence officers," he added. Salvini's Lega is a member of a club for European nationalists, called The Movement. This group was founded by Steve Bannon, the political strategist who previously worked for President Donald Trump, and by a nationalist Belgian politician called Mischael Modrikamen. When asked about his links to Russia, Modrikamen told CNBC last month: "I was invited a few years ago to Moscow, visited the Parliament, the Duma and so on." He also said that he had been invited to some events at the Russian embassy in Belgium, but has no relationship with the country apart from that.

How could Europe be targeted?

"What policymakers should be concerned about is actions by the Russian government to undermine democracy, gain economic leverage that can be used to further its broader foreign policy goals, or interfere in countries' domestic democratic political processes," Joshua Kirschenbaum, senior fellow at the Alliance for Securing Democracy, told CNBC. "The Russian uses opaque financial channels and strategic investments in furtherance of these aims, and in so doing it often exports corruption and criminality," he also said.

If there is [a nation] somewhere whose main political priority is to disintegrate Europe, this certainly is Russia. Donald Tusk European Council President