The campaign of French presidential candidate Emmanuel Macron says it has been the target of a “massive hacking attack” after a trove of documents was released online.
The campaign said that genuine files were mixed up with fake ones in order to confuse people.
It said it was clear that hackers wanted to undermine Mr Macron ahead of Sunday’s second round vote.
The centrist will face off against far-right candidate Marine Le Pen.
The documents were leaked on a file sharing website late on Friday and the Macron camp condemned the action just before the official campaigning period ended at midnight (22:00 GMT).
Candidates and the media now face restrictions until the polls close on Sunday evening, meaning Mr Macron cannot issue further statements.
Opinion polls had indicated the former economy minister carried a lead of 20 percentage points or more over Ms Le Pen, the National Front candidate.
What was released?
About nine gigabytes of data were posted online by an anonymous user.
Mr Macron’s En Marche movement said internal campaign documents, including emails and financial data, had been taken in an “act of massive, co-ordinated hacking”.
“The leaked files were obtained several weeks ago by hacking personal and professional email accounts of several officials of the movement,” it said in a statement.
The campaign said the documents showed only legitimate campaign activities.
France’s election commission warned that publication or republication of the leaked information could be a criminal offence.
How did the leaks spread?
The hashtag #MacronLeaks appeared on Twitter on an account used by a US alt-right figure on Friday afternoon – and was reportedly retweeted 87 times in the first five minutes, suggesting the use of automated bots to amplify the signal.
Within 90 minutes, the information had caught the attention of prominent supporters of Marine Le Pen and was further spread by bots.
Some three-and-a-half hours after the initial tweet, #MacronLeaks had been used some 47,000 times and the prominent Wikileaks account played a key role in publicising the hashtag.
Who might be responsible?
That too remains unclear. The Macron camp has not blamed any specific party but said the hack clearly aimed to damage it and undermine French democracy,
It compared it to the leak of Democratic Party emails in last year’s US presidential election that was blamed on Russian hackers.
Wikileaks, which published those emails, posted a link to the Macron documents on Twitter but implied it was not responsible.
Is this unprecedented?
Mr Macron’s team has already been the victim of hacking attacks, for which it has blamed groups based in Russia and Ukraine. It suspects the Kremlin of wanting to help Ms Le Pen, who supports a pro-Moscow foreign policy.
- Macron campaign servers went down for several minutes in February after attacks apparently originating in Ukraine
- Last month security experts from the company Trend Micro said that Russian hackers were targeting Mr Macron’s campaign, using phishing emails, malware and fake net domains in an attempt to grab login names, passwords and other credentials of campaign staff
Russia has denied that it is behind attacks aimed at Mr Macron.
On Thursday, the centrist candidate filed a lawsuit over online rumours that he had a secret bank account in the Caribbean.
Mr Macron called the allegations “fake news and lies” and said some of the sites spreading them were “linked to Russian interests”.