During a brawling presidential debate this week, far-right candidate Marine Le Pen raised an issue against centrist rival Emmanuel Macron that has spiraled into accusations regarding Russian hackers and the notorious 4chan website.

The issue concerned the long-whispered rumored that Macron, a former investment banker and Economic Minister, had opened an offshore bank account in the Bahamas to dodge taxes. He has denied this previously, and there has been no proof that would contradict him.

Still, the issue has lingered around the margins because it speaks to attempts by supporters of Le Pen’s populism to paint Macron as an out-of-touch elitist.

The presidential debate on Wednesday grew heated as the moderators lost control, with both candidates tearing into each other just a few days before the final vote on Sunday. At one point, Le Pen retorted: “Pay attention to what you say, Mr. Macron. I hope we will not learn that you had an offshore account in the Bahamas.”

The timing, and the mention of the Bahamas specifically, came just a few hours after an anonymous 4chan user posted screen shots of documents supposed to prove that Macron had set up a company in the Bahamas to avoid taxes.

“The first doc is the incorporation of a shell company in Nevis, a country that doesn’t keep ownership records of corporations,” the user wrote. “The second is proof of a banking relationship with a bank involved in tax evasion in the Cayman Islands. People have known for a while that Macron underreported his income and assets to the government, but nobody knew where it was stored. Here’s where his money is stored. See what you can do with this, anon. Let’s get grinding. If we can get #MacronCacheCash trending in France for the debates tonight, it might discourage French voters from voting Macron.”

Macron’s campaign issued a statement later in the evening saying the documents were clearly not real and that the attempt to spread information was “fake news” intended to influence voters. Moreover, the campaign accused followers of Russian president Vladimir Putin and U.S. president Donald Trump of being behind the forgeries.

“Here is how a fake news makes its way in a few hours to the heart of the French presidential campaign,” said the statement of Macron’s En Marche! campaign.

On Thursday, French media reported that Macron’s campaign had filed an official complaint and that a French prosecutor had launched an investigation. In a subsequent radio interview, Le Pen insisted she had not accused Macron but rather had simply asked a question about the issue.

The issue once again stoked fear about the impact of “fake news” and attempts by outside groups to sway voters.

Learning a lesson from the U.S. presidential election, a number of French media figures have joined together with Google and Facebook to develop Crosscheck, a project to identify and weed out fake news pertaining to the election. And Facebook said it has cracked down on 30,000 fake accounts during the French election season.

With two days to go before the French return to the ballot box, Macron retains a comfortable lead in most polls and is widely expected to win. However, some uncertainty remains because an unusually large number of French voters have said they plan to abstain, particularly those who had supported more left-wing candidates.