Mr. Macron’s En Marche movement says leaked documents have been mixed with false documents to “seed doubt and disinformation”.

The campaign of French presidential candidate Emmanuel Macron said it suffered a “massive and coordinated” hacking attack and document leak that it called a bid to destabilise Sunday’s presidential run-off.

Fears of hacking, fake news manipulation and Russian meddling clouded the French campaign but had largely gone unrealised until late Friday’s admission by Mr. Macron’s campaign that it had suffered a coordinated online pirate attack had led to the leak of campaign emails and financial documents. It was unclear who was behind the hack and the leak.

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A campaign blackout starting minutes after the Macron team announcement means that Marine Le Pen’s campaign can’t legally comment on the leak.

In a statement, Mr. Macron’s En Marche movement said the hack took place a few weeks ago, and that the leaked documents have been mixed with false documents to “seed doubt and disinformation” and destabilise Sunday’s presidential run-off. Hillary Clinton’s U.S. presidential campaign suffered similar leaks, and also said that authentic documents were mixed with false documents.

Watchdog examines leak

France’s election campaign watchdog said it is investigating the hacking attack.

The commission overseeing the campaign said in a statement it is holding a meeting Saturday after the late-night leak on Friday. It warned that some of the leaked documents are “probably” fake.

The timing of the leak could be seen as either bizarre or inspired.

The documents’ release just before France enters a roughly two-day-long blackout — during which politicians, journalists and even ordinary citizens are meant to pull back from any public election talk to avoid swaying the vote — means that the leak may have very little impact beyond the overheated world of Twitter and Reddit.

On the other hand, the messages’ release just before France’s political machinery shuts down for the weekend might mean that talk of the leak — regardless of its veracity — will dominate dinner table conversations as French voters make up their minds on Saturday.

Some experts see the Macron document dump as yet another sign of a “post-truth” society, one in which fake news, exaggerated tales and partisan talking points can crowd aside objective facts.

Dan Gillmor, a journalism professor at Arizona State University, calls it a global “war on reality” waged by partisans aiming to undermine public trust in, well, just about everything.

“One of their clear goals is to help demagogues and authoritarians who have contempt for democratic principles,” he said via email.

The candidates stopped campaigning at midnight on Friday to give voters a day of reflection before the election. It’s a stark choice — Ms. Le Pen’s anti-immigration, anti-European Union platform, or Mr. Macron’s progressive, pro-E.U. stance.

Tensions marred the race right to the end.

France’s presidential voting watchdog called on the Interior Ministry late Friday to look into claims by the Le Pen campaign that ballot papers are being tampered nationwide to benefit Mr. Macron. The Le Pen campaign said electoral administrators in several regions who receive ballot papers for both candidates have found the Le Pen ballot “systematically torn up”.

Earlier in the day, anti-Le Pen crowds disrupted her visit to a renowned cathedral in Reims.

The presidential campaign has been unusually bitter, with voters hurling eggs and flour, protesters clashing with police and candidates insulting each other on national television a reflection of the widespread public disaffection with politics as usual.

Ms. Le Pen, 48, has brought her far-right National Front party, once an outcast for its racism and anti-Semitism, closer than ever to the French presidency, seizing on working-class voters’ growing frustration with globalisation and immigration. Even if she loses, she is likely to be a powerful opposition figure in French politics in the upcoming parliamentary election campaign.

In an interview with The Associated Press in the final hours of a hostile, topsy-turvy campaign, Ms. Le Pen said that win or lose, “we changed everything.” She claimed an “ideological victory” for her populist, anti-immigrant world view.

“Even if we don’t reach our goal, in any event there is a gigantic political force that is born,” she told AP in her campaign headquarters. Her party “imposed the overhaul” of French politics and set the tone of the election, she said.

The 39-year-old Mr. Macron, too, played a key role in upending France’s traditional political structure with his wild-card campaign.

Voters liked the idea, and chose Mr. Macron and Ms. Le Pen in the first-round vote, dumping the traditional left and right parties that have governed modern France. Ms. Le Pen said those parties have been “blackballed”.

Many voters, however, don’t like either Ms. Le Pen or Mr. Macron. They fear her party’s racist past, while worrying that his platform would demolish worker job protections or be too much like his mentor, the deeply unpopular outgoing President Francois Hollande.