Hackers backed by the Iranian government recently tried to hack email accounts used by the campaign of a US presidential candidate, a Microsoft official said on Friday.

The “Phosphorous” hackers, as Microsoft has named the group, targeted the unidentified campaign by attempting to access email accounts campaign staff received through Microsoft cloud services. Rather than relying on malware or exploiting software vulnerabilities, the attackers worked relentlessly to gather information that could be used to activate password resets and other account recovery services Microsoft provides.

“Highly motivated”

The attacks on the campaign were part of a major offensive by Phosphorous that—over a 30-day period from August to September—made more than 2,700 attempts to identify consumer email accounts belonging to targeted individuals. Besides campaign staff, targeted accounts also belonged to current and former US government officials, journalists covering global politics, and prominent Iranians living outside of Iran. Of the more than 2,700 attempts to identify accounts, 241 of them were attacked. The attacks resulted in the successful compromise of four accounts, none of which belonged to the campaign.