What is MacronLeaks?
At 8.36pm Paris time on Friday an anonymous person posted nine gigaoctets of emails, accounts and other documents from Macron's election campaign on the US-based 4Chan web forum.
The giant leak came shortly before campaigning ended in the final round of the French presidential election, soliciting a response from the Macron camp just minutes before announcements by the candidates and their supporters would have broken electoral law.
Who was behind it?
4Chan is used by the American far right and was also the site on which accusations that Macron had a secret bank account in the Bahamas appeared just hours before his final TV debate with his far-right rival Marine Le Pen, who referred to the rumour during the confrontation.
The first person to publish a link to the dump on Twitter was Jack Posobiec, a supporter of US President Donald Trump who runs the far-right site The Rebel and was instrumental Pizzagate, the false accusation that US presidential Hillary Clinton's campaign director ran a paedophile ring from a Washington pizzeria.
It was then retweeted by William Craddick, the first person to tweet the Bahamas account rumour, which was retweeted by Posobiec.
Wikileaks then published a leak to the documents, while warning that it could be a practical joke.
Responding to an appeal Posobiec, a French user tweeted several messages about the leaks at 9.20pm French time, to be taken up by supporters of Le Pen's National Front and then by party officials, who tweeted at 11.44pm, 11.49pm and 11.54pm, just minutes before the midnight deadline for campaigning.
The hashtag #MacronLeaks was tweeted 47,000 times in the first three and a half hours after Prosobiec first used it, according to the Digital Forensic Research Lab of the Atlantic Council.
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The US-based company Flashpoint claims to have found traces of the APT 28 group, which is close to Russian military intelligence, and the Trend Micro company says that pro-Kremlin Russian pirates had started to take an interest in the Macron campaign but other experts said at the weekend that it was too early to reach a conclusion on Russian involvement.
How damaging is it?
The Macron campaign responded angrily just before midnight, saying it was a "massive hack" aimed at "democratic destabilisation, like that seen during the last presidential campaign in the United States".
At first it declared that most of the material was genuine but that fakes had been inserted to discredit Macron.
While admitting that it had not done a complete search, WikiLeaks said it had found no fakes.
Senior Le Pen aide Florian Philippot suggested on Twitter that the leak might contain information the media had deliberately suppressed.
The Macron campaign later said that "the documents arising from the hacking are all lawful and show the normal functioning of a presidential campaign", although social media users seem to have added other fakes since the publication.
The leak does not seem to have had a major effect on the outcome of the election but right-wing social media users seem confident it will to do so in the near future.
Why have French media reported little on the content of MacronLeaks?
French media have reported the event but said little on the content of the documents dump, sparking accusations of pro-Macron bias by right-wing social media users.
But there are several reasons, starting with the fact that it contains masses of information, most of it completely anodyne.
There are also legal considerations.
French electoral law forbids broadcasters, and to a lesser extent newspapers, to cite election propaganda from midnight Friday to the end of polling on Sunday.
And France's electoral authority warned at the weekend that publication of information from it could lead to prosecution, since it had been illegally acquired.
Does it have implications outside France?
Britain has a general election on 8 June and Germany has one on 24 September.German Social Democrat leader Martin Schulz has already been subject to an online campaign falsely alleging that his father was a concentration camp commandant.
If, as Macron's supporters claim, the hack is part of a wider campaign to discredit Western democracy, there may be more hacks ahead.