State-backed hackers from China have targeted staffers working on the US presidential campaign of Democrat Joe Biden, a senior Google security official said on Thursday.
The same official said Iranian hackers had recently targeted email accounts belonging to Republican President Donald Trump's campaign staff.
The announcement, made on Twitter by the head of Google's Threat Analysis Group, Shane Huntley, is the latest indication of the digital spying routinely aimed at top politicians, Reuters reported.
Huntley said there was "no sign of compromise" of either campaign.
Iranian attempts to break into Trump campaign officials' emails have been documented before. Last year, Microsoft Corp announced that a group often nicknamed Charming Kitten had tried to break into email accounts belonging to an unnamed US presidential campaign, which sources identified as Trump's.
Earlier this year, the threat intelligence company Area 1 Security said Russian hackers had targeted companies tied to a Ukrainian gas firm where Biden's son once served on the board.
Google declined to offer details beyond Huntley's tweets, but the unusually public attribution is a sign of how sensitive Americans have become to digital espionage efforts aimed at political campaigns.
"We sent the targeted users our standard government-backed attack warning and we referred this information to federal law enforcement," a Google representative said.
Hacking to interfere in elections has become a concern for governments, especially since US intelligence agencies concluded that Russia ran a hacking and propaganda operation to disrupt the American democratic process in 2016 to help then-candidate Trump become president. Among the targets was digital infrastructure used by 2016 Democratic presidential candidate Hillary Clinton's campaign.
