"With respect to potential computer intrusion by hostile actors, we did not find direct evidence that Secretary Clinton’s personal e-mail domain, in its various configurations since 2009, was successfully hacked. But, given the nature of the system and of the actors potentially involved, we assess that we would be unlikely to see such direct evidence. We do assess that hostile actors gained access to the private commercial e-mail accounts of people with whom Secretary Clinton was in regular contact from her personal account. We also assess that Secretary Clinton’s use of a personal e-mail domain was both known by a large number of people and readily apparent. She also used her personal e-mail extensively while outside the United States, including sending and receiving work-related e-mails in the territory of sophisticated adversaries. Given that combination of factors, we assess it is possible that hostile actors gained access to Secretary Clinton’s personal e-mail account."
https://www.fbi.gov/news/press-releases/press-releases/statement-by-fbi-director-james-b-comey-on-the-investigation-of-secretary-hillary-clinton2019s-use-of-a-personal-e-mail-system