"The En Marche! Movement has been the victim of a massive and coordinated hack this evening which has given rise to the diffusion on social media of various internal information," the statement said.
A campaign blackout starting minutes after the Macron team announcement at midnight Friday means that Le Pen's campaign can't legally comment on the leak, Fox News reported. An interior minister also declined to comment, citing French rules that forbid any commentary liable to influence an election, Reuters reported. The ban remains in place until the polls close Sunday at 8 p.m.
Opinion polls show independent centrist Macron winning with about 62 percent of the vote, Reuters reported.
The Kremlin has denied it was behind any such attacks, even though Macron's camp renewed complaints against Russian media and a hackers' group operating in Ukraine.
Vitali Kremez, director of research with New York-based cyber intelligence firm Flashpoint, told Reuters his review indicates that APT 28, a group tied to the GRU, the Russian military intelligence directorate, was behind the leak. He cited similarities with U.S. election hacks that have been previously attributed to that group.
"If indeed driven by Moscow, this leak appears to be a significant escalation over the previous Russian operations aimed at the U.S. presidential election, expanding the approach and scope of effort from simple espionage efforts towards more direct attempts to sway the outcome," Kremez said.
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 killed?"
Macron spokesman Sylvain Fort, in a response on Twitter, called Philippot's tweet “vile.”