"Emmanuel Macron is the only candidate in the French presidential campaign to be targeted," Macron's "En Marche!" party said in a statement, Reuters reported.
"It's no coincidence if Emmanuel Macron, the last remaining progressive candidate in this election is the priority target."
Macron's campaign cited as evidence the results of a study by security firm Trend Micro, which said it had found proof that the spy group, dubbed "Pawn Storm", had target its campaign.
Pro-European centrist Emmanuel Macron and Le Pen claimed the most votes in the Sunday election to make it through to a second round run-off on May 7.
Ahead of the presidential election, Macron's campaign had accused Russia of using hacking and fake news to interfere with the French vote.