France is seeking to keep a computer hack of frontrunner Emmanuel Macron's campaign emails from influencing the country's presidential election with a warning it could be an offence to republish the data.
Mr Macron's team said on Saturday a "massive" hack had dumped emails, documents and campaign financing information online just before campaigning ended on Friday and France entered a quiet period which forbids politicians commenting on the leak.
"On the eve of the most important election for our institutions, the commission calls on everyone present on internet sites and social networks, primarily the media but also all citizens, to show responsibility and not pass on this content, so as not to distort the sincerity of the ballot," the French election commission said.
The data leak emerged as polls predicted Mr Macron was on course for a comfortable victory over far-right leader Marine Le Pen in Sunday's election, with the last surveys showing his lead widening to about 62 percent to 38.
The commission, which supervises the electoral process, said after a hastily called meeting on Saturday the data been fraudulently obtained and could be mixed with false information.
However its rules may be difficult to enforce in an era where people get much of their news online, information flows freely across borders and many users are anonymous.
French media covered the hack in various ways, with left-leading Liberation giving it prominence on its website but television news channels opting not to mention it.
As much as nine gigabytes of data were posted on a profile called EMLEAKS to Pastebin, a site allowing anonymous document sharing, late on Friday.
It was not immediately clear who was responsible but Mr Macron's political movement said in a statement the hack was an attempt to destabilise democracy and to damage the party.
"The En Marche! (Onwards!) Movement has been the victim of a massive and co-ordinated hack," it said.
En Marche! said the leaked documents dealt with the normal operations of a campaign and included some information on campaign accounts. It said the hackers had mixed false documents with authentic ones to "sow doubt and disinformation".
France is the latest nation to see a major election overshadowed by allegations of cyber hacking after US intelligence agencies said in January Russian President Vladimir Putin had ordered hacking of parties tied to Democratic candidate Hillary Clinton to influence the election on behalf of Republican Donald Trump.
The Kremlin has denied it was behind any such attacks, although Mr Macron's camp renewed complaints against Russian media and a hackers' group operating in Ukraine.
Sunday's election is seen as the most important in France for decades, with two diametrically opposed views of Europe and the country's place in the world at stake.
The National Front's Le Pen would close borders and quit the euro currency, while independent Mr Macron wants closer European co-operation and an open economy.
On Friday night as the #Macronleaks hashtag buzzed around social media, Florian Philippot, deputy leader of the National Front, tweeted "Will Macronleaks teach us something that investigative journalism has deliberately kept silent?"
Vitali Kremez, director of research with New York-based cyber intelligence firm Flashpoint, said his review indicated APT 28, a group tied to the GRU, the Russian military intelligence directorate, was behind the leak.