Staff with the Japanese anti-virus firm Trend Micro have added more details to previous suggestions that the centrist politician was being singled out for electronic eavesdropping by the Kremlin.
The campaign’s digital chief, Mounir Mahjoubi, confirmed the attempted intrusions but said they had all been thwarted.
“It’s serious, but nothing was compromised,” he said.
Mr Macron faces far-right rival Marine Le Pen in France’s presidential run-off on May 7. Mr Macron favours a strong European Union, while Ms Le Pen wants to pull France out of the bloc, weakening it.
Trend Micro said it discovered the campaign by monitoring the creation of rogue, lookalike websites often used by hackers to trick victims into giving up their passwords.
The Tokyo-based firm recently detected four Macron-themed fake domains being set up on digital infrastructure used by a group it calls Pawn Storm, according to Trend Micro researcher Feike Hacquebord.
Mr Mahjoubi confirmed that at least one of the sites had recently been used as part of an attempt to steal campaign staffers’ online credentials.
Unmasking which group is behind spying campaigns is one of the most challenging aspects of cybersecurity, but Mr Hacquebord said he was confident Trend Micro’s conclusions are correct.
Mr Hacquebord said: “This is not a 100% confirmation, but it’s very, very likely.”
He added that the political nature of the targeting was “really in line with what they’ve been doing in the last two years”.
Trend Micro has stopped short of accusing any country of pulling Pawn Storm’s strings, but American spy agencies and a variety of threat intelligence firms say that Pawn Storm, an extraordinarily prolific group also known as Fancy Bear or APT28, is an arm of Russia’s intelligence apparatus.
French officials have also tended to be more circumspect than their American counterparts, repeatedly declining to tie Pawn Storm to any specific body.
Russian government officials have long denied claims of state-sanctioned hacking. On Monday, Kremlin spokesman Dmitry Peskov was quoted as saying that the notion that Russian hackers were targeting the French election was “completely incorrect”.
Mr Mahjoubi said the attempts to penetrate the Macron campaign date back to December. In February, the campaign complained publicly of being targeted by Russia-linked electronic spying operations, although it offered no proof at the time.
Trend Micro’s report, which was produced independently of the Macron campaign and lists 160 electronic espionage operations across a series of targets, adds a measure of evidence to the notion, even if the fact that the rogue websites were registered in March and April does not line up with the campaign’s timeline.
The French election, the first round of which Mr Macron won Sunday with just over 24% of the vote, has been closely watched for signs of digital interference of any kind.
Many observers feared a repeat of the US electoral contest in 2016, when hackers allegedly backed by Moscow broke into the email inboxes of the Democratic National Committee and other political operatives.
Pilfered documents subsequently appeared on WikiLeaks and other more mysterious websites, putting the Democrats on the defensive during their losing campaign against Donald Trump.