The prosecutor's office in Paris has begun a preliminary investigation into whether so-called fake news is being used to influence voting in the May 7 French presidential election.
The announcement on May 4 came after centrist presidential candidate Emmanuel Macron, who is favored to win the election, filed a lawsuit.
Macron filed the suit after his far-right rival, Marine Le Pen, suggested in a televised debate on May 3 that he could be holding an offshore account in the Bahamas.
During the debate, she said, "I hope we won't find out you have an offshore account in the Bahamas."
Le Pen appeared to be referring to two sets of apparent forgeries -- published a couple of hours before the debate -- that purported to show Macron was involved with a Caribbean bank and a firm based on the island of Nevis.
Le Pen quickly backed off her comments after the reports were shown to be fake.
In the documents, a signature alleged to be Macron's didn't match the one he uses. Other inaccuracies also undermined the anonymous posting.
Macron is a former investment banker, and Le Pen has often attacked him over his business interests.