Hackers with ties to Russia, China and Iran are attempting to snoop on people and groups involved with the US 2020 presidential election, Microsoft says.
The Russian hackers who breached the 2016 Democratic campaign are again involved, said the tech firm.
Microsoft said it was "clear that foreign activity groups have stepped up their efforts" targeting the election.
Both President Donald Trump and Democrat Joe Biden's campaigns are in the cyber-raiders' sights.
What did Microsoft say?
Russian hackers from the Strontium group have targeted more than 200 organisations , many of which are linked to US political parties - both Republicans and Democrats, Microsoft said in a statement.
Strontium is also known as Fancy Bear, a cyber-attack unit allegedly affiliated with Russian military intelligence, the GRU.
"Similar to what we observed in 2016, Strontium is launching campaigns to harvest people's log-in credentials or compromise their accounts, presumably to aid in intelligence gathering or disruption operations," said Tom Burt, a Microsoft vice-president in charge of customer security and trust.
The firm said Chinese hackers had launched attacks targeting individuals connected to Mr Biden's campaign, while Iranian hackers had continued efforts targeting people associated with the Trump campaign.
Most of the cyber-attacks had not been successful, according to Microsoft. The attacks have also not been launched on groups that handle the voting systems themselves.
"What we've seen is consistent with previous attack patterns that not only target candidates and campaign staffers but also those they consult on key issues," Mr Burt said.
"These activities highlight the need for people and organisations involved in the political process to take advantage of free and low-cost security tools to protect themselves as we get closer to election day."
Microsoft reported that Chinese groups had launched attacks on the personal email accounts of people affiliated with the Biden campaign, as well as "at least one prominent individual formerly associated with the Trump Administration".
