Just hours before France's ill-tempered presidential debate on Wednesday, trolls and bots on Twitter began spreading unsubstantiated claims that centrist candidate Emmanuel Macron had a secret offshore bank account.
Mr Macron's campaign immediately accused his far-right opponent Marine Le Pen of enjoying patronage from the masters of online dark arts — Vladimir Putin's Kremlin, previously accused of interfering in last year's US polls. For his part, Mr Putin has frequently said that Russia does not interfere in elections elsewhere.
Ahead of Sunday's run-off in France, there has been speculation about the extent of Mr Putin's influence. In Wednesday's debate, Mr Macron accused Ms Le Pen of being "subject to the diktats of Mr Putin".
Over the past several years, the Russian leader and the far-right politician, who share a similar nationalist outlook, have developed close ties. These links have been cemented by complex financial arrangements and overwhelmingly positive coverage of Ms Le Pen in the Russian state-backed media.
For the Russian leader, a victory for Ms Le Pen would offer an opportunity to sow dissent in the west. Mr Putin's backing has helped the French politician present herself as a global leader.
"We are being vigilant about any attempts by foreign powers to influence this election," said a senior French intelligence official. "It is clear that Russia is sympathetic to Le Pen in the election."
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Ms Le Pen's allies in the National Front and Moscow say that her ties to Russia and the support she enjoys there reflect a natural affinity with the Kremlin rather than any systematic or organised covert subversion campaign. "We share a similar vision of the world," says Bertrand Dutheil de La Rochère, an FN strategist.
These ties have become so close that Ms Le Pen met Mr Putin in a surprise visit to Moscow in March. Given that FN's other foreign allies are limited to fellow far-right parties, this was seen as a coup for the French politician.
Florian Philippot, Ms Le Pen's deputy, said the meeting proved Ms Le Pen was a "global politician".