After months of trying to move the political needle in favour of Marine Le Pen in the French presidential election, American far-right activists on Saturday threw their weight behind a hacking attack against her rival, Emmanuel Macron, hoping to cast doubt on an election that is pivotal to France and the wider world.

The efforts were the culmination of a months-long campaign against Mr Macron after his candidacy began to gain steam this year, with digital activists in the United States and elsewhere regularly sharing tactics, tips and tricks across the English- and French-speaking parts of the internet.

It is unclear whether the leaked documents, which some experts say may be connected to hackers linked to Russia, will affect the outcome of the election Sunday between Ms Le Pen, the far-right candidate from the National Front, and Mr Macron, an independent centrist. But the role of American far-right groups in promoting the breach online highlights their growing resolve to spread extremist messages beyond the United States.

“It’s the anti-globalists trying to go global,” said Ben Nimmo, a senior fellow of the digital forensics research lab at the Atlantic Council, a think tank, who has studied the far right’s recent efforts against Macron and others in France. “There’s a feeling of trying to export the revolution.”

The digital attack, which involved posting campaign documents like emails and accounting records to message boards, occurred late Friday, hours before a legal prohibition on campaign communications went into effect across France. In response, Mr Macron’s team said the hackers had included fake information alongside authentic material “to sow doubt.”

“Intervening in the final hour of the official campaign, this operation is clearly a matter of democratic destabilisation, as was seen in the United States during the last presidential campaign,” Mr Macron’s campaign said in a statement late Friday, minutes before the communications prohibition went into effect.

Yet within hours after the hacked documents were made public, the hashtag #MacronLeaks began trending worldwide, aided by far-right activists in the United States who have been trying to sway the French vote in favour of Ms Le Pen.

Jack Posobiec, a journalist with the far-right news outlet The Rebel, was the first to use the hashtag with a link to the hacked documents online, which was then shared more widely by WikiLeaks. Mr Posobiec remains the second-most mentioned individual on Twitter in connection with the hashtag behind WikiLeaks, according to a review of the past 100,000 Twitter posts published since late Friday.

While there is no evidence that the breach against Macron’s campaign was organised by this loosely connected group of far-right campaigners, the US activists have been gathering on sites like 4chan and Discord, which were previously used to coordinate support for Donald Trump’s presidential campaign.

One popular tactic, experts say, has been “Twitter raids,” or efforts to hijack trending hashtags and topics on the social media site and inject far-right and anti-Macron propaganda.

A week before the second round of the French election, for instance, online activists, many from the United States and other English-speaking countries, flooded Twitter with coordinated anti-Macron memes — online satirical photos with often biting captions — carrying hashtags like #elysee2017 that were linked to the campaign. That included portraying him as a 21st-century equivalent of Marie Antoinette, the out-of-touch last queen of France, and other memes made allegations of an extramarital affair.

“They tried to bombard French Twitter with memes favorable to Le Pen,” said Padraic Ryan, a project coordinator at Storyful, an online marketing company that tracks social media activity around news events. “The campaigns are showing an increasing level of sophistication and coordination.”

Just days before the last French presidential debate, an anonymous user on 4chan, whose message boards include anti-Semitic, white supremacist and other far-right discussions, posted what were said to be copies of documents showing that Mr Macron had supposedly set up a bank account in the Bahamas to avoid paying taxes. He denied the allegations.

Ms Le Pen referred to such an overseas bank account during the vicious debate, leading to a bitter rebuttal by Mr Macron’s team and an official investigation into the spread of the rumours.

The reports were followed with another accusation, also posted on 4chan, hours before Mr Macron’s campaign was subjected to the online leak, that he had bank accounts in the Cayman Islands. There is no evidence that he has such accounts.

Despite these increasingly coordinated digital efforts by far-right activists, analysts say, their efforts had not reached the vast majority of the French electorate — until the Friday release of the hacked documents.

It will most likely take until after the election to review all the leaked documents. Under France’s strict electoral rules, any publication of the material before polling day may lead to charges.

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As the French readied themselves for the election Sunday, discussion on social media — both in favour and in opposition of leaking the documents — began to swirl, according to a review of Twitter data.

Since late Friday, Twitter hashtags related to the leak have topped the trending charts for France, a sign that people are talking about the leak, although most of the discussion has been limited to members of the far-right community who already support Ms Le Pen.

Yet in a sign of how the far right outside the country is also trying foment the discussion, many of the Twitter posts about the hacking have originated in the United States, according to Trendsmap, a data analytics tool. About half the social media messages around political hashtags linked to the breach have been written in English, based on a review of Trendsmap data, as activists outside France have helped to spread news of the leak.

The top 25 Twitter posts shared with the hashtag #MacronLeaks were written in English, according to Mr Nimmo of the Atlantic Council, with many of the online accounts reposting links set up as bots, or automated accounts controlled by third-party individuals.

“That has helped to push this leak entirely into the camp of the alt-right,” Mr Nimmo said Saturday about the online far-right community in the United States.

The origin of the leaks in France is still not known. The French media has been ordered by the electoral commission not to publish their contents. But the growth of digital misinformation and other falsities is likely to only grow amid a season of elections in Europe in which British and German voters will soon head to the polls, said Janis Sarts, director of the NATO Strategic Communications Center of Excellence, a think tank in Riga, Latvia.

“Misinformation is increasingly used to achieve political ends,” Mr Sarts said. “Technology helps to amplify that message through fake news sites and social media.”